Operations on memory cells

ABSTRACT

In an example, a plurality of signal pulses is applied across a plurality of memory cells concurrently until each respective memory cell reaches a desired state. Each respective memory cell is commonly coupled to a first signal line and is coupled to a different respective second signal line. Each signal pulse causes each respective memory cell to move toward the desired state by causing each respective memory cell to snap back. Current to a respective second signal line is turned off in response to each time the respective memory cell coupled thereto snaps back.

PRIORITY INFORMATION

This application is a Continuation of U.S. application Ser. No.15/827,119, filed on Nov. 30, 2017, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to memory, and, moreparticularly, to operations on memory cells.

BACKGROUND

Memory devices may typically be provided as internal, semiconductor,integrated circuits in computers or other electronic devices. There arevarious types of memory including volatile and non-volatile memory.

Various memory arrays can be organized in a cross-point architecturewith memory cells (e.g., two terminal cells) being located atintersections of a first and second signal lines used to access thecells (e.g., at intersections of word lines and bit lines). Some memorycells can be, for example, resistance variable memory cells whose state(e.g., stored data value) depends on the programmed resistance of thememory cell. Some resistance variable memory cells can comprise a selectelement (e.g., a diode, transistor, or other switching device) in serieswith a storage element (e.g., a phase change material, metal oxidematerial, and/or some other material programmable to differentresistance levels). Some variable resistance memory cells, which may bereferred to as self-selecting memory cells, comprise a single materialwhich can serve as both a select element and a storage element for thememory cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a three-dimensional view of an example of a memory array, inaccordance with a number of embodiments of the present disclosure.

FIG. 2A illustrates threshold voltage distributions associated withmemory states of memory cells, in accordance with a number ofembodiments of the present disclosure.

FIG. 2B is an example of a current-versus-voltage curve corresponding toa memory state of FIG. 2A, in accordance with a number of embodiments ofthe present disclosure.

FIG. 2C is an example of a current-versus-voltage curve corresponding toanother memory state of FIG. 2A, in accordance with a number ofembodiments of the present disclosure.

FIG. 3 illustrates an example of voltage signals that can applied to amemory cell in association with comparing input data to data stored inthe memory cell, in accordance with a number of embodiments of thepresent disclosure.

FIG. 4 illustrates an example of comparing input data to data stored ina memory array, in accordance with a number of embodiments of thepresent disclosure.

FIG. 5 illustrates an example of a portion of a memory array andassociated circuitry, in accordance with a number of embodiments of thepresent disclosure.

FIG. 6 illustrates another example of a portion of a memory array andassociated circuitry, in accordance with a number of embodiments of thepresent disclosure.

FIG. 7A presents example timing diagrams, in accordance with a number ofembodiments of the present disclosure.

FIG. 7B shows an operation being performed on a portion of a memoryarray, in accordance with a number of embodiments of the presentdisclosure.

FIG. 8A presents example timing diagrams, in accordance with a number ofembodiments of the present disclosure.

FIG. 8B shows an operation being performed on a portion of a memoryarray, in accordance with a number of embodiments of the presentdisclosure.

FIG. 9A illustrates an example of data store operation, in accordancewith a number of embodiments of the present disclosure.

FIG. 9B illustrates examples of write voltages, in accordance with anumber of embodiments of the present disclosure.

FIG. 9C illustrates an example of a current pulse, in accordance with anumber of embodiments of the present disclosure.

FIG. 10A illustrates another example of a data store operation, inaccordance with a number of embodiments of the present disclosure.

FIG. 10B presents example timing diagrams, in accordance with a numberof embodiments of the present disclosure.

FIG. 11 illustrates a portion of a memory array and associatedcircuitry, in accordance with a number of embodiments of the presentdisclosure.

FIG. 12 is a block diagram illustrating an example of an apparatus, inaccordance with a number of embodiments of the present disclosure.

DETAILED DESCRIPTION

In an example, a plurality of signal pulses is applied across aplurality of memory cells concurrently until each respective memory cellreaches a desired state. Each respective memory cell is commonly coupledto a first signal line and is coupled to a different respective secondsignal line. Each signal pulse causes each respective memory cell tomove toward the desired state by causing each respective memory cell tosnap back. Current to a respective second signal line is turned off inresponse to each time the respective memory cell coupled thereto snapsback.

A number of embodiments of the present disclosure provide benefits. Forexample, using a plurality of pulses to program a memory cell may allowthe energy delivered to the cells to be adjusted during each snapbackevent that may lead to a reduction in the overall energy consumptionduring programming compared to previous methods where a continuousvoltage differential might be applied. This may also allow the overallenergy delivered to the cells to be adjusted by adjusting the number ofsnapback events. In some examples, turning off the current to a cellduring each snapback may also reduce power consumption compared to notturning off the current.

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown, byway of illustration, specific examples. In the drawings, like numeralsdescribe substantially similar components throughout the several views.Other examples may be utilized and structural and electrical changes maybe made without departing from the scope of the present disclosure. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present disclosure is defined onlyby the appended claims and equivalents thereof.

FIG. 1 is a three-dimensional view of an example of a memory array 100(e.g., a cross-point memory array), in accordance with a number ofembodiments of the present disclosure. Memory array 100 may include aplurality of first signal lines (e.g., first access lines), which may bereferred to as word lines 110-0 to 110-N, and a plurality second signallines (e.g., second access lines), which may be referred to as bit lines120-0 to 120-M that cross each other (e.g., intersect in differentplanes). For example, each of word lines 110-0 to 110-N may cross bitlines 120-0 to 120-M. A memory cell 125 may be between the bit line andthe word line (e.g., at each bit line/word line crossing).

The memory cells 125 may be resistance-variable memory cells, forexample. The memory cells 125 may include a material programmable todifferent data states. In some examples, each of memory cells 125 mayinclude a material that may act as a selector material (e.g., aswitching material) and a storage material, so that each memory cell 125may act as both a selector device and a memory element. For example,each memory cell may include a chalcogenide material that may be formedof various doped or undoped materials, that may or may not be aphase-change material, and/or that may or may not undergo a phase changeduring reading and/or writing the memory cell. In some examples, eachmemory cell 125 may include a ternary composition that may includeselenium (Se), arsenic (As), and germanium (Ge), a quaternarycomposition that may include silicon (Si), Se, As, and Ge, etc.

In various embodiments, the threshold voltages of memory cells 125 maysnap back in response to a magnitude of an applied voltage differentialacross them exceeding their threshold voltages. Such memory cells may bereferred to as snapback memory cells. For example, a memory cell 125 maysnap back from a non-conductive (e.g., high-impedance) state to aconductive (e.g., lower impedance) state in response to the appliedvoltage differential exceeding the threshold voltage. For example, amemory cell snapping back may refer to the memory cell transitioningfrom a high-impedance state to a lower impedance state responsive to avoltage differential applied across the memory cell being greater thanthe threshold voltage of the memory cell. A threshold voltage of amemory cell snapping back may be referred to as a snapback event, forexample.

FIG. 2A illustrates threshold distributions associated with variousstates of memory cells, such as memory cells 125 (e.g., state 0, state1, and state D), in accordance with a number of embodiments of thepresent disclosure. In FIG. 2A, the voltage VCELL may correspond to avoltage differential applied to (e.g., across) the memory cell, such asthe difference between a bit line voltage (VBL) and a word line voltage(VWL) (e.g., VCELL=VBL−VWL). The threshold voltage distributions (e.g.,ranges) 200-1, 200-2, 201-1, 201-2, 202-D1, and 202-D2 may represent astatistical variation in the threshold voltages of memory cellsprogrammed to a particular state. The distributions illustrated in FIG.2A correspond to the current versus voltage curves described further inconjunction with FIGS. 2B and 2C, which illustrate snapback asymmetryassociated with assigned data states.

In some examples, the magnitudes of the threshold voltages of a memorycell 125 in a particular state may be asymmetric for differentpolarities, as shown in FIGS. 2A, 2B and 2C. For example, the thresholdvoltage of a memory cell 125 may have a different magnitude in onepolarity than in an opposite polarity. For example, an applied voltagemagnitude sufficient to cause a memory cell 125 to snap back can bedifferent (e.g., higher or lower) for one applied voltage polarity thanthe other.

In various embodiments, the threshold voltage of a memory cell may drift(e.g., to a higher absolute value) over time, as indicated by thresholddistributions 202-D1 and 202-D2, that may be referred to as driftedstates. For example, a memory cell programmed to a distribution 201-2may drift toward distribution 202-D2 over time. Similarly, a memory cellprogrammed to a distribution 200-2 may also drift to a higher thresholdvoltage over time.

A memory cell programmed to a distribution 200-1 may drift towarddistribution 202-D1 over time. A memory cell programmed to distribution201-1 may also drift toward a higher threshold voltage in a negativesense over time.

FIG. 2A illustrates demarcation voltages VDM1 and VDM2, which can beused to determine the state of a memory cell (e.g., to distinguishbetween state “1” and state “0” as part of a read operation). In thisexample, VDM1 is a positive voltage used to distinguish cells in state 1(201-2) from cells in state 0 (200-2) or drifted state 202-D2.Similarly, VDM2 is a negative voltage used to distinguish cells in state0 (200-1) from cells in state 1 (201-1) or drifted state 202-D1. In theexamples of FIGS. 2A-2C, a memory cell 125 in a positive state 0 doesnot snap back in response to applying VDM1; a memory cell 125 in apositive state 1 snaps back in response to applying VDM1; a memory cell125 in a negative state 0 snaps back in response to applying VDM2; and amemory cell 125 in a negative state 1 does not snap back in response toapplying VDM2.

Embodiments are not limited to the example shown in FIG. 2A. Forexample, the designations of state 0 and state 1 can be interchanged(e.g., distributions 201-1 and 201-2 can be designated as state 0 anddistributions 200-1 and 200-2 can be designated as state 1).

In some examples, cell threshold voltage drift may be acceleratedelectrically and/or thermally. For example, an electric field and/orheat may be applied to the memory cell to accelerate drift. In someexamples, a memory cell 125 may be programmed to state 0 or state 1 fromthe drift state.

FIGS. 2B and 2C are examples of current-versus-voltage curvescorresponding to the memory states of FIG. 2A, in accordance with anumber of embodiments of the present disclosure. As such, in thisexample, the curves in FIGS. 2B and 2C correspond to cells in whichstate 0 is designated as the higher threshold voltage state in aparticular polarity (positive polarity direction in this example), andin which state 1 is designated as the higher threshold voltage state inthe opposite polarity (negative polarity direction in this example). Asnoted above, the state designation can be interchanged such that state 1could correspond to the higher threshold voltage state in the positivepolarity direction with state 0 corresponding to the higher thresholdvoltage state in the negative direction.

FIGS. 2B and 2C illustrate snapback as described herein. VCELL canrepresent an applied voltage across the memory cell. For example, VCELLcan be a voltage applied to a top electrode corresponding to the cellminus a voltage applied to a bottom electrode corresponding to the cell(e.g., via a respective word line and bit line). As shown in FIG. 2B,responsive to an applied positive polarity voltage (VCELL), a memorycell programmed to state 0 (e.g., 200-2) is in a non-conductive stateuntil VCELL reaches voltage Vtst02, at which point the cell transitionsto a conductive (e.g., lower resistance) state. This transition can bereferred to as a snapback event, which occurs when the voltage appliedacross the cell (in a particular polarity) exceeds the cell's thresholdvoltage. Accordingly, voltage Vtst02 can be referred to as a snapbackvoltage. In FIG. 2B, voltage Vtst01 corresponds to a snapback voltagefor a cell programmed to state 0 (e.g., 200-1). That is, as shown inFIG. 2B, the memory cell transitions (e.g., switches) to a conductivestate when VCELL exceeds Vtst01 in the negative polarity direction.

Similarly, as shown in FIG. 2C, responsive to an applied negativepolarity voltage (VCELL), a memory cell programmed to state 1 (e.g.,201-1) is in a non-conductive state until VCELL reaches voltage Vtst11,at which point the cell snaps back to a conductive (e.g., lowerresistance) state. In FIG. 2C, voltage Vtst12 corresponds to thesnapback voltage for a cell programmed to state 1 (e.g., 201-2). Thatis, as shown in FIG. 2C, the memory cell snaps back from a highimpedance non-conductive state to a lower impedance conductive statewhen VCELL exceeds Vtst12 in the positive polarity direction.

In various instances, a snapback event can result in a memory cellswitching states. For instance, if a VCELL exceeding Vtst02 is appliedto a state 0 cell, the resulting snapback event may reduce the thresholdvoltage of the cell to a level below VDM1, which would result in thecell being read as state 1 (e.g., 201-2). As such, in a number ofembodiments, a snapback event can be used to write a cell to theopposite state (e.g., from state 1 to state 0 and vice versa).

As described further herein below, the threshold voltage distributionscorresponding to programmed states can be asymmetric across polarities(e.g., different for forward/positive and reverse/negative biases). Thedesignation of different states to the higher threshold voltages inopposite polarities (e.g., the higher threshold voltage in the forwarddirection being designated as state 0 and the higher threshold voltagein the reverse direction being designated as state 1) can be exploitedto perform in memory compute functions in accordance with embodimentsdescribed herein. For instance, in a number of embodiments, memory cellscan be operated to implement an XOR (exclusive or) function. PerformingXOR functions can be used, for example, to perform comparison operationsto determine whether input data (e.g., an input vector) matches datastored in an array. In a number of embodiments, XOR functions can beused to perform higher order operations such as addition, subtraction,multiplication, division, etc.

FIG. 3 illustrates an example of voltage signals that can applied to amemory cell in association with comparing input data to data stored inthe memory cell, in accordance with a number of embodiments of thepresent disclosure. FIG. 3 includes a memory cell 325, which can be amemory cell such as memory cell 125 described above. The memory cell 325is coupled to a word line (WL) 310 and a bit line (BL) 320. A voltagesignal SBL is applied to bit line 320 and a voltage signal SWL isapplied to word line 310, where a difference between voltage signal SBLand voltage signal SWL corresponds to a voltage differential appliedacross memory cell 325. Analogous to FIGS. 2A-2C, the example shown inFIG. 3 corresponds to cells in which the higher threshold voltage in theforward (e.g., positive polarity) direction is designated as state 0 andthe higher threshold voltage in the reverse direction (e.g., negativepolarity) is designated state 1. Accordingly, a positive voltagedifferential VDM1 is used to determine cell state in the forwarddirection and a negative differential VDM2 is used to determine cellstate in the reverse direction. In a number of embodiments, input states(e.g., data values) can be mapped to the designated voltage demarcationlevels (e.g., VDM1 and VDM2) in order to compare input data values tostored data values, which can implement an XOR function, for example.

For instance, voltage signal SWL may have a voltage VWL1 and voltagesignal SBL may have a voltage VBL1 such that an applied voltagedifferential VDM1 (e.g., VDM1=VBL1−VWL1) can correspond to an inputstate 0 (e.g., a logic 0), or voltage signal SWL may have a voltage VWL2and voltage signal SBL may have a voltage VBL2 such that an appliedvoltage differential VDM2 (e.g., VDM2=VBL2−VWL2) can correspond to aninput state 1 (e.g., a logic 1). For example, when state 0 is the inputstate (e.g., a state to be compared to a stored state of a cell), theinput voltage differential applied to (e.g., across) memory cell 325 maybe VDM1 (e.g., with the bit line 320 being driven high to voltage VBL1and the word line 310 being driven low to voltage VWL1). When state 1 isthe input state, the input voltage differential applied to memory cell325 may be VDM2 (e.g., with the bit line 320 being driven low to voltageVBL2 and the word line 310 being driven high to voltage VWL2).Accordingly, the polarity of the applied VDM1 signal is opposite thepolarity of the VDM2 signal.

With reference to the threshold distributions shown in FIG. 2A formemory cells having snapback characteristics such as that shown in FIGS.2B and 2C, an input state 0 can be compared to the stored state of amemory cell (e.g., 325) by applying the corresponding input voltagesignal (e.g., VDM1) to the cell and determining (e.g., sensing) whetheror not a snapback event occurs. Similarly, an input state 1 can becompared to the stored state of the memory cell by applying thecorresponding voltage signal (e.g., VDM2) to the cell and sensingwhether or not a snapback event occurs. Table 1 below is a truth tableillustrating an example in which the results of the comparisons of inputstates to stored states corresponds to an XOR function.

For instance, to determine whether an input state 0 matches a data statestored in a memory cell, VDM1 can be applied to the cell. If the cellstores state 0 (e.g., 200-2), or has drifted to state 202-D2, a snapbackevent will not occur (e.g., since VDM1 is below the threshold voltagelevel of the cell). If the cell stores state 1 (e.g., 201-2) a snapbackevent will occur (e.g., since VDM1 is above the cell threshold voltagelevel). Accordingly, detection of a snapback event responsive to appliedvoltage VDM1 indicates a mismatch (e.g., the input data state 0 does notmatch the stored state 1), and lack of detection of a snapback eventresponsive to applied voltage VDM1 indicates a match (e.g., the inputstate 0 is the same as the stored data state or is in a drifted stateD). Similarly, to determine whether an input state 1 matches a datastate stored in a memory cell, VDM2 can be applied to the cell. If thecell stores state 0 (e.g., 200-1) a snapback event will occur (e.g.,since VDM2 is above the threshold voltage of the cell). If the cellstores state 1 (e.g., 201-1), or has drifted to state 202-D1, a snapbackevent will not occur (e.g., since VDM2 is below the cell thresholdvoltage level). Accordingly, detection of a snapback event responsive toapplied voltage VDM2 indicates a mismatch (e.g., the input data state 1does not match the stored state 0), and lack of detection of a snapbackevent responsive to applied voltage VDM2 indicates a match (e.g., theinput state 1 is the same as the stored data state or is in a driftedstate D).

Therefore, as shown below in Table 1, the results of the comparisonoperations correspond to an XOR function. That is, a match is determinedonly if the input state is the same as the stored state, and a mismatchis determined if the input state is different than the stored state.

In a number of embodiments, the drifted states 202-D1 and 202-D2 can beused in association with an additional input state (e.g., an input stateother than state 0 or state 1), which may be referred to as input stateZ (e.g., a “don't care” state). Since cells in a drifted state in eitherpolarity have a threshold voltage above the snapback voltage, nosnapback event will occur regardless of the applied voltage. Therefore,regardless of the stored state of the memory cell (e.g., state 0, state1, or a drifted state), no snapback event will be detected responsive tothe voltage signal SBL having a voltage VBLZ and the voltage signal SWLhaving a voltage VWLZ, and thus an applied voltage differential VDMZ(e.g., VDMZ=VBLZ−VWLZ). The voltage VDMZ may correspond to an inhibitvoltage having a magnitude between respective snapback voltages of thememory cells (in either polarity). In this example, lack of detection ofa snapback event corresponds to a “match” result.

Results of comparison operations including input state Z and driftedmemory state D are included in Table 1. As illustrated, the third inputstate Z (e.g., “don't care”) provides the ability to perform ternaryoperations, for example.

Table 1 is an example of a truth table corresponding to comparing inputdata to stored data as described in conjunction with FIGS. 2A-2C andFIG. 3.

TABLE 1 Result of comparing an input state to a state stored by a memorycell Input State Stored State Result 0 0 Match (no snapback) 0 1Mismatch (snapback) 1 0 Mismatch (snapback) 1 1 Match (no snapback) Z 0,1, D Match (no snapback) 0, 1, Z D Match (no snapback)

Although the examples previously described in conjunction with FIGS.2A-2C and FIG. 3 and the example in Table 1 use a determined snapbackevent to indicate a mismatch result and lack of a snapback event toindicate a match, embodiments are not so limited. For instance, in otherexamples, a determined snapback event may indicate a match while adetermined lack of a snapback event may indicate a mismatch.

FIG. 4 illustrates an example of comparing input data (e.g., a group ofinput bit values) to data (e.g., groups of bit values) stored in amemory array 400 in accordance with a number of embodiments of thepresent disclosure. The array 400 can include memory cells such as thosedescribed above. As shown in FIG. 4, the input data may be an inputvector 402 (e.g., “00110011” corresponding to bits Bit0 to Bit7 asshown) to be compared to data stored in memory array 400 (e.g., as bitvectors 404-0 to 404-7, which can be referred to collectively as bitvectors 404).

In this example, memory array 400 includes a plurality of first signallines (e.g., word lines) 410-0 to 410-7 and a plurality of second signallines (e.g., bit lines 420-0 to 420-7). The array 400 can be across-point array with a memory cell 425 located at each bit line/wordline crossing. Although eight bit lines and eight word lines are shownin the example of FIG. 4, embodiments are not limited to a particularnumber of word lines and/or bit lines.

In FIG. 4, the bit vectors 404 are stored in cells commonly coupled to arespective word line 410 (e.g., with bit 0 stored in a cell coupled tobit line 420-0, bit 1 coupled to bit line 420-1, . . . , bit 7 coupledto bit line 420-7). For instance, in this example, bit vector 404-0(“01111111”) is stored in cells coupled to word line 410-0, bit vector404-1 (“11110111”) is stored in cells coupled to word line 410-1, bitvector 404-2 (“11111111”) is stored in cells coupled to word line 410-2,bit vector 404-3 (“11111101”) is stored in cells coupled to word line410-3, bit vector 404-4 (“00110011”) is stored in cells coupled to wordline 410-4, bit vector 404-5 (“00000000”) is stored in cells coupled toword line 410-5, bit vector 404-6 (“11111110”) is stored in cellscoupled to word line 410-6, and bit vector 404-7 (“00000000”) is storedin cells coupled to word line 410-7.

As shown in FIG. 4, detectors, which can comprise a sense amplifier 430,are coupled to each respective word line 410. For example, senseamplifiers 430-0 to 430-7 may be respectively coupled to word lines410-0 to 410-7. In some examples, a sense amplifier 430 may be part of aword line driver (not shown in FIG. 4). A latch 440 may be coupled toeach respective sense amplifier 430, and thus each respective word line410. For example, latches 440-0 to 440-7 may be respectively coupled tosense amplifiers 430-0 to 430-7, and thus word lines 410-0 to 410-7.Latches 440-0 to 440-7 may respectively store data indicative of whethervectors 404-0 to 404-7 match input vector 402. In some examples, a senseamplifier 430 in combination with a respective latch 440 may be referredto as sensing circuitry.

As described above, comparing an input state 0 (e.g., bit value of 0) toa bit value stored in a memory cell (e.g., 425) can include applying thevoltage differential VDM1, as previously described, to that memory cell.For example, comparing Bit0 of the input vector 402 (e.g., input state0) to the bit value stored in the memory cell coupled to bit line 420-0and word line 410-0 (e.g., stored state 0) can include applying apositive polarity voltage differential VDM1 to the memory cell (e.g., byapplying the bit line voltage VBL1 to bit line 420-0 and the word linevoltage VWL1 to word line 410-0). Bit0 of the input vector 402 may becompared to the bit 0 data values of each of the stored vectors 404 byapplying the voltage differential VDM1 to each memory cell coupled tobit line 420-0. In some examples, while applying the bit line voltageVBL1 to bit line 420-0, the word line voltage VWL1 may be applied to theword lines 410-0 to 410-7 concurrently.

As used herein, multiple acts being performed concurrently is intendedto mean that each of these acts is performed for a respective timeperiod, and each of these respective time periods overlaps, in part orin whole, with each of the remaining respective time periods. In otherwords, those acts are concurrently performed for at least some period oftime.

In a similar manner, Bit1 of the input vector 402 (e.g., input state 0)can be compared to bit 1 of the stored data vectors 404 by applying thevoltage differential VDM1 to each memory cell coupled to bit line 420-1,Bit4 of the input vector 402 (e.g., input state 0) can be compared tobit 4 of the stored data vectors 404 by applying the voltagedifferential VDM1 to each memory cell coupled to bit line 420-4, andBit5 of the input vector 402 (e.g., input state 0) can be compared tobit 5 of the stored data vectors 404 by applying the voltagedifferential VDM1 to each memory cell coupled to bit line 420-5. In someexamples, the voltage differential VDM1 may be applied concurrently to(e.g., in parallel with) one or more memory cells coupled to bit lines420-0, 420-1, 420-4, and 420-5 during a first phase (e.g., time period),as shown in FIG. 4. For example, Bit0, Bit1, Bit4, and Bit5 of the inputvector 402 may be compared concurrently (e.g., in parallel) to bit 0,bit 1, bit 4, and bit 5, respectively, of the stored vectors 404 duringthe first phase. After the first phase, in an example, the voltagedifferential VDMZ, as described previously in conjunction with FIGS.2A-2C and FIG. 3, may be applied to concurrently (e.g., in parallel) toone or more memory cells coupled to bit lines 420-0, 420-1, 420-4, and420-5 during a second phase, as shown in FIG. 4.

Comparing an input state 1 (e.g., bit value of 1) to a bit value storedin a memory cell (e.g., 425) can include applying the voltagedifferential VDM2, as previously described, to that memory cell. Forexample, comparing Bit2 of the input vector 402 (e.g., input state 1) tothe bit value stored in the memory cell coupled to bit line 420-2 andword line 410-0 (e.g., stored state 1) can include applying a negativepolarity voltage differential VDM2 to the memory cell (e.g., by applyingthe bit line voltage VBL2 to bit line 420-0 and the word line voltageVWL2 to word line 410-0). Bit2 of the input vector 402 may be comparedto the bit 2 data values of each of the stored vectors 404 by applyingthe voltage differential VDM2 to each memory cell coupled to bit line420-0. In some examples, while applying the bit line voltage VBL2 to bitline 420-0, the word line voltage VWL2 may be applied to the word lines410-0 to 410-7 concurrently.

In a similar manner, Bit3 of the input vector 402 (e.g., input state 1)can be compared to bit 3 of the stored data vectors 404 by applying thevoltage differential VDM2 to each memory cell coupled to bit line 420-3,Bit6 of the input vector 402 (e.g., input state 1) can be compared tobit 4 of the stored data vectors 404 by applying the voltagedifferential VDM2 to each memory cell coupled to bit line 420-6, andBit7 of the input vector 402 (e.g., input state 1) can be compared tobit 7 of the stored data vectors 404 by applying the voltagedifferential VDM2 to each memory cell coupled to bit line 420-7. In someexamples, the voltage differential VDM2 may be applied concurrently to(e.g., in parallel with) one or more memory cells coupled to bit lines420-2, 420-3, 420-6, and 420-7 during a second phase (e.g., timeperiod), as shown in FIG. 4. For example, Bit2, Bit3, Bit6, and Bit7 ofthe input vector 402 may be compared concurrently (e.g., in parallel) tobit 0, bit 1, bit 4, and bit 5, respectively, of the stored vectors 404during the second phase.

In some examples, the voltage differential VDMZ may be appliedconcurrently to one or more memory cells coupled to bit lines 420-2,420-3, 420-6, and 420-7 during the first phase while VDM1 is beingapplied concurrently (e.g., in parallel) to one or more memory cellscoupled to bit lines 420-0, 420-1, 420-4, and 420-5, as shown in FIG. 4.During the second phase, the voltage differential VDMZ may be applied toconcurrently to one or more memory cells coupled to bit lines 420-0,420-1, 420-4, and 420-5 while the voltage differential VDM2 may beapplied concurrently to one or more memory cells coupled to bit lines420-2 420-3, 420-6, and 420-7. In other examples, the comparisonsdescribed in FIG. 4 may occur in a single phase in which VDM1 is appliedto bit lines 420-0, 420-1, 420-4, and 420-5 (e.g., those bit linescoupled to cells whose stored data value is to be compared to inputstate 0) concurrently with VDM2 being applied to bit lines 420-2, 420-3,420-6, and 420-7 (e.g., those bit lines coupled to cells whose storeddata value is to be compared to input state 1).

For a stored vector 404 to match input vector 402, each respective bitvalue stored in that vector must match a corresponding one of the bitvalues in input vector 402 (e.g., all the bit values Bit0 through Bit7of input vector 402 must match the bit values of respective bits 0through 7 of the stored vector 404). As described above, in a number ofembodiments, a match between a value of a bit of input vector 402 and abit value stored by a memory cell may be determined by not sensing asnapback in response to the applied voltage differential (e.g., VDM1 orVDM2 depending on whether the input state being compared is state 0 orstate 1). A mismatch between an input bit value and a bit value storedby a memory cell may be determined by sensing a snapback in response tothe applied voltage differential.

In a number of embodiments, detection circuits (e.g., sense amplifiers)coupled to the word lines and/or bit lines of an array can be configuredto latch a particular data value (e.g., “0”) responsive to sensing asnapback event on a corresponding signal line (e.g., word line or bitline) and to latch another data value (e.g., “1”) responsive to notsensing a snapback event on the corresponding signal line. For instance,in the example of FIG. 4, the detection circuits coupled to the wordlines 410 include respective sense amplifiers 430 and correspondinglatches 440. In this example, a latched value of “1” indicates nosnapback event was detected on the word line, and a latched value of “0”indicates that a snapback event was detected on the word line.Therefore, the comparison operation described in FIG. 4 results in onlylatch 440-4 storing a “1,” since stored vector 404-4 (e.g., 00110011) isthe only one of stored vectors 404 that matches the input vector 402(e.g., 00110011). It is noted that, each of the other stored vectors 404include at least one bit whose value does not match the correspondingbit of the input vector 402. Accordingly, the detection circuits coupledto each of the other word lines 410 (e.g., all word lines except forword line 410-4) will detect at least one snapback event during thecomparison operation and will therefore latch a “0” as shown in FIG. 4(e.g., to indicate at least one mismatch).

As described further below, in a number of embodiments, the detectioncircuits can provide a feedback signal (e.g., to a driver) in responseto the snapback of a memory cell (e.g., in response to sensing asnapback event) in order to prevent further current flow through theword line, which may prevent other memory cells coupled to the word linefrom snapping back. Preventing further current flow through a word lineresponsive to sensing a snapback event can conserve power, and reducesensing time, among other benefits. For example, in the comparisonoperation described in FIG. 4, a snapback of any one cell coupled to aparticular word line 410 results in a determined mismatch for thecorresponding stored vector 404. Once a mismatch is determined (e.g.,via sensing of a single snapback event), further current flow throughthe corresponding word line is unnecessary.

In some examples, the configuration in FIG. 4 may operate as a contentaddressable memory (CAM), such as a ternary content addressable memory(TCAM) (e.g., owing to the ability of the memory cells to implementternary functions). In other examples, the configuration in FIG. 4 mayoperate as a Hopfield network, a spiking network, and/or a sparsedistributed memory.

FIG. 5 illustrates an example of a portion of a memory array 500 andassociated detection circuitry for performing comparison operations inaccordance with a number of embodiments of the present disclosure.Memory array 500 may be a portion of memory array 100 and/or memoryarray 400. Memory cell 525 is coupled to a word line 510 and a bit line520 and may be operated as described herein.

The example shown in FIG. 5 includes a driver 550 (e.g., a word linedriver 550) coupled to word line 510. Word line driver 550 may supplybi-polar (e.g., positive and negative) current and/or voltage signals toword line 510. A sense amplifier 530, which may comprise a cross-coupledlatch, is coupled to word line driver 550, and may detect positive andnegative currents and/or positive and negative voltages on word line510. In some examples, sense amplifier 530 may be part of (e.g.,included in) word line driver 550. For example, the word line driver 550may include the sensing functionality of sense amplifier 530. A bit linedriver 552 is coupled to bit line 520 to supply positive and/or negativecurrent and/or voltage signals to bit line 520.

The sense amplifier 530 and word line driver 550 are coupled to a latch540, which can be used to store a data value indicating whether or not asnapback event of cell 525 has occurred responsive to an applied voltagedifferential. For instance, an output signal 554 of sense amplifier 530is coupled to latch 540 such that responsive to detection, via senseamplifier 530, of memory cell 525 snapping back, the output signal 554causes the appropriate data value to be latched in latch 540 (e.g., adata value of “1” or “0” depending on which data value is used toindicate a detected snapback event). As an example, if a latched datavalue of “1” is used to indicate a detected snapback event, then signal554 will cause latch 540 to latch a data value of logical 1 responsiveto a detected snapback of cell 525, and vice versa.

When a positive voltage differential VDM1 (e.g., corresponding to aninput state 0) is applied to memory cell 525 (e.g., the word linevoltage VWL1 is low and the bit line voltage VBL1 is high) and memorycell 525 stores state 1, voltage differential VDM1 may be greater thanthe threshold voltage Vtst12 (FIG. 2C), and memory cell 525 may snapback to a conductive state, causing the positive current flow, shown inFIG. 2C, through memory cell 525 from bit line 520 to word line 510.Sense amplifier 530 may detect this current, and/or a voltage associatedtherewith, for example, and may output signal 554 to latch 540 inresponse to detecting this current and/or voltage. For example, signal554 may indicate to latch 540 (e.g., by having a logical low value) thatcurrent is positive, and thus that word line voltage is low. In responseto the signal 554 indicating that the word line voltage is low, latch540 may output a signal 556 (e.g. voltage) to circuitry 558 of orcoupled to word line driver 550 that turns off (e.g., inhibits) thecurrent flow through word line 510, and thus through memory cell 525.

In examples, when a negative voltage differential VDM2 (e.g.,corresponding to an input state 1) is applied to memory cell 525 (e.g.,the word line voltage VWL2 is high and the bit line voltage VBL2 is low)and memory cell 525 stores state 0, voltage differential VDM2 is greater(in a negative sense) than the threshold voltage Vtst01 (FIG. 2B), andmemory cell 525 may snap back to a conductive state, causing thenegative current flow, shown in FIG. 2B, through memory cell 525 fromword line 510 to bit line 520. Sense amplifier 530 may detect thiscurrent, and/or a voltage associated therewith, for example, and mayoutput the signal 554 to latch 540 in response to detecting this currentand/or a voltage. For example, signal 554 may indicate to latch 540 thatcurrent is negative (e.g., by having a logical high value), and thusthat word line voltage is high. In response to the signal 554 indicatingthat the word line voltage is high, latch 540 may output a signal 560(e.g. voltage) to circuitry 562 of or coupled to word line driver 550that turns off the current flow through word line 510. In some examples,sense amplifier 530 in combination with circuitries 558 and 562 may bereferred to as detection circuitry.

FIG. 6 illustrates an example of a portion of a memory array 600 andassociated detection circuitry for performing comparison operations(e.g. for detecting and recording snapback) in accordance with a numberof embodiments of the present disclosure. Memory array 600 may be aportion of memory array 100 and/or memory array 400. A memory cell 625is coupled to word line 610 and a bit line 620 and may be operated asdescribed herein.

A word line driver 650 is coupled to word line 610, and a bit linedriver 652 is coupled to bit line 620. Word line driver 650 outputs asignal (e.g., a voltage) SIN1 to sense amplifier 630-1 (e.g., adetector) and a signal (e.g., a voltage) SIN2 to sense amplifier 630-2.A latch 640 is coupled to feedback circuitries (e.g., sense amplifiers)630-1 and 630-2. Sense amplifier 630-1 generates and outputs a signal(e.g., a voltage) IPULS1 to latch 640, and sense amplifier 630-2generates and outputs a signal (e.g., a voltage) IPULS2 to latch 640. Insome examples, latch 640 has a static-random-access-memory (SRAM)configuration.

In some examples, sense amplifiers 630-1 and 630-2 are feedback latches,such as cross-coupled latches, that operate as inverters. For example,when the input to sense amplifier 630-1, SIN1, is high, the output ofsense amplifier 630-1, IPULS1, may be low and vice versa. When the inputto sense amplifier 630-2, SIN2, is low, the output of sense amplifier630-2, IPULS2, is high and vice versa.

Circuitry (e.g., transistors) 660 of sense amplifier 630-1 incombination with circuitry (e.g., transistors) 662-1 of latch 640 actsas a comparator, for example, where transistors 660 act as a pull-downand circuitry (e.g., transistors) 662-1 may act as a load. Circuitry(e.g., transistors) 665 of sense amplifier 630-2 in combination withcircuitry (e.g., transistors) 662-2 of latch 640 act as a comparator,for example, where transistors 665 may act as a pull-up and transistors662-2 may act as a load.

The signals IPULS1 and IPULS2 also act as feedback signals that act toturn off the current to word line 610. For example, when the signal SIN1is high, the signal IPULS1 is low and causes a transistor 668 of senseamplifier 630-1 to turn off, and thus turn off current flow to word line610, and thus to memory cell 625. For example, transistor 668, and thussense amplifier 630-1, are configured to selectively decouple (e.g.,electrically isolate) node 674 from word line 610 in response to signalIPULS1 going low. When the signal SIN2 is low, the signal IPULS2 is highand may cause a transistor 670 of sense amplifier 630-2 to turn off, andthus turn off current flow to word line 610. For example, transistor670, and thus sense amplifier 630-2, are configured to selectivelydecouple node 678 from word line 610 in response to signal IPULS2 goinghigh.

In an example, when the signal IPULS1 is low, it causes data in latch640 to change its value (e.g., from a logical 1 to a logical 0), andwhen the signal IPULS2 is high, it causes data in latch 640 to changeits value (e.g., from a logical 1 to a logical 0).

When a positive voltage differential VDM1 (e.g., corresponding to aninput state 0) is applied to memory cell 625 (e.g., the word linevoltage VWL1 is low and the bit line voltage VBL1 is high) and memorycell 625 stores state 1, voltage differential VDM1 is greater than thethreshold voltage Vtst12 (FIG. 2C), and memory cell 625 snaps back to aconductive state, causing the positive current flow, shown in FIG. 2C,through memory cell 625 from bit line 620 to word line 610.

Arrow 672 in FIG. 6 shows an example of the current path in response tomemory cell 625 snapping back in response to voltage differential VDM1.In general, the current flows from bit line 620, through memory cell625, and to word line 610. The current flows through word line 610 toword line driver 650 and from word line driver 650 to a (e.g., low)voltage node 674 that may be at a voltage SLL, such as ground. Forexample, the word line voltage VWL1 may be at the voltage SLL

The snapback of memory cell 625 in response to voltage differential VDM1causes the signal SIN1 (e.g., that may be low initially) to be (e.g., togo) high. Sense amplifier 630-1 causes the signal IPULS1 (e.g., that maybe high initially) to be (e.g., to go) low. The low value IPULS1 maycause latch 640 to store (e.g., to latch) logical 0, indicative ofmemory cell 625 snapping back. The low value of IPULS1 (e.g., operatingas a feedback signal) also causes transistor 668 to turn off the currentflow to word line 610. Transistor 668 may be on initially, for example,in response to IPULS1 being high initially.

For example, to apply VDM1 to memory cell 625, driver 650 and senseamplifier 630-1 couple node 674 and the voltage SLL to word line 610while a voltage greater than voltage SLL is applied to bit line 620. Inresponse to memory cell 625 snapping back, current initially flows frombit line 620 to node 674 until SIN1 goes high (e.g., in response to theword line voltage going high responsive to memory cell 625 snappingback) and IPULS1 goes low and causes sense amplifier 630-1 to decouplenode 674 from word line 610.

In examples, when a negative voltage differential VDM2 (e.g.,corresponding to an input state 1) is applied to memory cell 625 (e.g.,the word line voltage VWL2 is high and the bit line voltage VBL2 is low)and memory cell 625 stores state 0, voltage differential VDM2 is greaterin a negative sense than the threshold voltage Vtst01 (FIG. 2B), andmemory cell 625 snaps back to a conductive state, causing the negativecurrent flow, shown in FIG. 2B, through memory cell 625 from word line610 to bit line 620.

Arrow 676 shows an example of the current path in response to memorycell 625 snapping back (e.g., in response to application of VDM2 acrossthe cell with the word line voltage being high). In general, the currentflows from a (e.g., high) voltage node 678 that is at a voltage SHH toword line driver 650, from word line driver 650 to word line 610, andfrom word line 610 to memory cell 625. The current may flow from wordline 610 through memory cell 625 to bit line 620. In some examples, theword line voltage VWL2 might be at the voltage SHH.

The snapback of memory cell 625 in response to voltage differential VDM2may cause the signal SIN2 (e.g., initially high) to be (e.g., to go)low. Sense amplifier 630-2 may cause the signal IPULS2 (e.g., that maybe low initially) to be (e.g., to go) high. The high value of IPULS2 maycause latch 640 to store (e.g., to latch) a logical 0, indicative ofmemory cell 625 snapping back. The high value of IPULS2 (e.g., operatingas a feedback signal) may also cause transistor 670 to turn off thecurrent flow to word line 610. Transistor 670 may be on initially, forexample, in response to IPULS2 being low initially.

For example, to apply VDM2 to memory cell 625, driver 650 and senseamplifier 630-2 may couple node 678 and the voltage SHH to word line 610while a voltage less than the voltage SHH is applied to bit line 620. Inresponse to memory cell 625 snapping back, current may initially flowfrom node 678 to bit line 620 until SIN2 goes low (e.g., in response tothe word line voltage going high in a negative sense responsive tomemory cell 625 snapping back) and IPULS2 goes high and causes senseamplifier 630-2 to decouple node 678 from word line 610.

Switching circuitry 680 may be used to set the operating ranges of latch640. For example, switching circuitry 680 may set the operating range oflatch 640 to be between the voltage SLL and a voltage MID, which may bemidway between the voltage SLL and SHH, in response to applying thevoltage differential VDM1 to memory cell 625 when the word line voltageis low. Switching circuitry 680 may, for example, set the operatingrange of latch 640 to be between the voltage MID and the voltage SHH inresponse to applying the voltage differential VDM2 to memory cell 625when the word line voltage is high. In some examples, switchingcircuitry 680 may be coupled to the latches that may be coupled to otherword lines. For example, latches 440-0 to 440-7 in FIG. 4 may becommonly coupled to switching circuitry 680. In some examples, thesensing circuitry that may include sense amplifiers 630-1 and 630-2 incombination with latch 640 may further include switching circuitry 680.

A transistor 682, such as a current-setting transistor, of senseamplifier 630-1 may be used to control (e.g., limit) the current flow inword line 610, and thus through memory cell 625, in response to signals(e.g., voltages) from a line 684 when the word line voltage is low. Atransistor 686, such as a current-setting transistor, of sense amplifier630-2 may be used to control (e.g., limit) the current flow in word line610 in response to signals (e.g., voltages) from a line 688 when theword line voltage is high. A line 690 may be used to convey the datastored in latch 640 to input/output circuitry, such as I/O circuitry1212 in FIG. 12. In some examples, in response to the current reaching aparticular level, transistors 682 and 686 act to limit the current,allowing an increase in the voltage (e.g., the magnitude of the voltage)of word line 610.

In some examples, transistors 668 and 682 in combination may be referredto as circuitry of sense amplifier 630-1, and transistors 670 and 686 incombination may be referred to as circuitry of sense amplifier 630-2. Insome examples, the transistors in sense amplifier 630-1 may be n-channeltransistors and the transistors in sense amplifier 630-2 may bep-channel transistors. Driver 650 may be configured to selectivelycouple word line 610 to sense amplifiers 630-1 and 630-2, for example.

FIG. 7A presents example timing diagrams associated with performingcomparison operations (e.g., that may include sensing operations) inaccordance with a number of embodiments of the present disclosure. FIG.7B is an example of a portion of a memory array 700 on which anoperation is being performed, and may be a portion of memory array 100or memory array 400, in accordance with a number of embodiments of thepresent disclosure. The timing diagrams in FIG. 7A can correspond to anoperation performed on the array of FIG. 7B (e.g., an operation in whicha voltage V1 is applied to the word line WL and a voltage V2 is appliedto each of the bit lines BL0 and BL1).

FIGS. 7A and 7B are used to illustrate an example of turning off currentto a memory cell, and thus to a word line, in response to detecting amismatch between data in only one memory cell coupled to a word line.For example, the current to the word line may be turned off in responseto detecting the snapback of the first memory cell of a group of memorycells commonly coupled to the word line to snap back. This, for example,may take advantage of the possibility that memory cells that might storethe same data state might have slightly different threshold voltages(e.g., that may be within the threshold distribution for that datastate) that might be less than an input voltage differential applied tothose memory cells. For example, the memory cells may snapback atdifferent times in response to the same input voltage differential. Insome examples, the first memory cell to snap back might be the memorycell with the lowest threshold voltage, and the current to the word linemight be turned off in response to detecting the snapback of that memorycell, thereby avoiding the need to detect the snapback of other memorycells. This may act to reduce the power consumption associated with notturning the current to the word line off after detecting a singlesnapback.

In some examples, the input voltage differential may be variable. Forexample, the input voltage differential may be a ramp voltagedifferential that may, for example, increase in magnitude (e.g., at aconstant rate) from a ground voltage (e.g., zero volts) to a voltagethat is greater in magnitude than a highest expected threshold voltageof the memory cells. In other examples, the variable input voltage maybe a ramped input voltage differential comprising a series of increasing(e.g., in magnitude) differential voltage pulses.

In the examples of FIGS. 7A and 7B, a memory cell MC0 at a crossing ofword line WL and bit line BL0 may be programmed to a threshold voltageVt0 (e.g., about 5.0 volts), and memory cell MC1 at a crossing of wordline WL and bit line BL1 may be programmed to a threshold voltage Vt1(e.g., about 5.1 volts) that is greater than threshold voltage Vt0.Memory cells MC0 and MC1 may be similar to (e.g., the same as) memorycells 125. For example, memory cells MC0 and MC1 may be programmed tothe state 1 shown in FIGS. 2A and 2C. The threshold voltages Vt0 and Vt1may be in the threshold-voltage distribution 201-2, corresponding thepositive state 1, shown in FIG. 2A, for example.

Initially, word line WL and bit lines BL0 and BL1 may be at a voltage V0(e.g., about 3.5 volts), so the voltage differential between bit lineBL0 and word line WL, and thus applied to memory cell MC0, and thevoltage differential between bit line BL1 and word line WL, and thusapplied to memory cell MC1, may initially be about zero (0) volt. Avoltage (e.g. level) V1 may then be applied to word line WL. The wordline voltage signal VWL may represent the instantaneous word linevoltage of word line WL. For example, the voltage signal VWL maydecrease from the initial voltage V0 to the voltage V1 in response toapplying V1 to word line WL.

A voltage V2 (e.g., about 5.5 volts) may be applied to bit lines BL0 andBL1 concurrently (e.g., after applying voltage V1 to word line WL).However, the present disclosure is not limited to applying the voltageV2 after applying the voltage V1. For example, the voltages V1 and V2might be applied at the same time or voltage V2 might be applied beforevoltage V1.

The voltage differential VDM1, such as a sensing voltage differential,between bit line BL0 and word line WL, and thus applied to memory cellMC0, may be VDM1=V2−V1 (e.g., about 5.5 volts). The voltage differentialVDM1 may also be between bit line BL1 and word line WL, and thus may beapplied to memory cell MC1. In some examples, voltage V2 may be avariable voltage of increasing magnitude, such as a ramp voltage ofincreasing magnitude or a series of voltage pulses of increasingmagnitude. For example, voltage V2 may have an initial value equal tothe voltage V1. Therefore, the voltage differential VDM1 may be a rampvoltage differential of increasing magnitude or a series of increasingdifferential voltage pulses of increasing magnitude (e.g., having astarting voltage of zero volts). FIGS. 7A and 7B may depict a sensingoperation, where a sensing differential, such as voltage differentialVDM1, is applied to memory cells MC0 and MC1 commonly coupled to a wordline WL and respectively coupled to bit lines BL0 and BL1.

The example of FIGS. 7A and 7B may depict a comparison operation whereVDM1 corresponds to a positive input state 0 compared to positive states1 stored in memory cells MC0 and MC1. For example, input states (e.g.,data) may correspond to components of an input vector and the statesstored by memory cells MC0 and MC1 are components of a stored vectorbeing compared to the input vector. Timing diagrams similar to those inFIG. 7A may depict a comparison operation where a negative input state 1might be compared to negative states 0 stored in memory cells MC0 andMC1 by applying VDM2 (FIG. 2A) to memory cells MC0 and MC1 such asvoltage VDM1.

The voltage differential VDM1 may be greater than the threshold voltageVt0 of memory cell MC0 and the threshold voltage Vt1 of memory cell MC1,for example, and thus may cause memory cells MC0 and MC1 to snap back.The threshold voltages of the memory cells at crossings of the remainingbit lines and the word line may be greater than the voltage differentialVDM1. In examples, the voltage differential VDM1 may be increased fromzero volt to threshold voltage Vt0 and to the threshold voltage Vt1(e.g., by increasing the voltage V2).

A bit line voltage signal VBL0 may represent the instantaneous bit linevoltage of bit line BL0, and a bit line voltage signal VBL1 mayrepresent the instantaneous bit line voltage of bit line BL1. Forexample, voltage signals VBL0 and VBL1 may increase concurrently fromthe voltage V0 to a voltage V3 in response to applying the voltage V2 tobit lines BL0 and BL1. For example, the difference VBL0−VWL may be theinstantaneous voltage differential across memory cell MC0, and thedifference VBL1−VWL may be the instantaneous voltage differential acrossmemory cell MC1.

The threshold voltage Vt0 of memory cell MC0 may, for example, beVt0=V3−V1 (e.g., about 5 volts) that may be less than voltagedifferential VDM1. The current signal IMC0, representative of theinstantaneous current flow through memory cell MC0, and the currentsignal IMC1, representative of the instantaneous current flow throughmemory cell MC1, may remain at a current I0 (e.g., about 0 amp) while(e.g., during the time) the word line voltage signal VWL decreases tothe voltage V1 and while (e.g., during the time) the bit line voltagesignals VBL0 and VBL1 increase to the voltage V3. For example, this maybe because during these times memory cells MC0 and MC1 are off (e.g.,are in their non-conductive states).

The voltage signal IPULS1 in FIG. 7A may be the output voltage signal ofsensing circuitry 730 coupled to word line WL in FIG. 7B. Sensingcircuitry 730 may be similar to (e.g., the same as) the sensingcircuitry described previously in conjunction with FIG. 5 and/or FIG. 6.For example, the voltage signal IPULS1 may remain at an initial presetvoltage V6 (e.g., about 3.5 volts), corresponding to a logical 1, whilethe word line voltage signal VWL decreases to the voltage V1 and whilethe bit line voltage signals VBL0 and VBL1 increase to the voltage V3.

Memory cell MC0 may snap back in response to the bit line voltage signalVBL0 reaching the voltage V3 while the word line voltage signal VWL isat the voltage V1. In response to memory cell MC0 snapping back, the bitline voltage signal VBL0 may decrease from voltage V3 to a voltage V4(e.g., about 4.5 volts); the word line voltage signal VWL may increasefrom voltage V1 to a voltage V5 (e.g., about one (1) volt) while the bitline voltage VBL0 decreases from voltage V3 to voltage V4; and thecurrent signal IMC0 may increase from the current I0 to a current I1.Note, for example, that as described previously in conjunction with FIG.2C, the voltage differential across a memory cell may decrease and thecurrent may increase as a result of the memory cell snapping back.

The voltage signal IPULS1 may decrease from the voltage V6 to a voltageV7 (e.g., about 0 volts), such as a logic 0, in response to sensingcircuitry 730 detecting the increase in the voltage of word line voltagesignal VWL. The sensing circuitry 730 may act to turn off the current toword line WL in response to voltage signal IPULS1 decreasing to voltagelevel V7. For example, sensing circuitry 730 may act to decouple wordline WL from a voltage node (e.g., causing word line WL to float).

Turning off the current to word line WL may act to prevent memory cellMC1 from snapping back, for example, when the voltage differentialacross memory cell MC1 becomes greater than the threshold voltage Vt1 ofmemory cell MC1, and thus memory cell MC1 may remain off and the currentsignal IMC1 may remain at the current I0. For example, the comparisonbetween the input data and the data stored in memory cells may beterminated in response to memory cell MC0 snapping back, thus preventingthe comparison to the data stored in memory cell MC1.

In some examples, after memory cell MC0 snaps back and the current onword line is turned off, the voltage differential VDIF between bit lineBL0 and word line WL, and thus across memory cell MC0, may beVDIF=V2−V8. The voltage differential VDIF may also be between bit lineBL1 and word line WL, and thus across memory cell MC1. For example,voltage differential VDIF may be less than the threshold voltages ofmemory cells MC0 and MC1.

In some examples, when the same voltage differential is applied tomemory cells MC0 and MC1, memory cell MC0 may snap back first, in thatmemory cell MC0 may have a lower threshold voltage than memory cell MC1.The current to word line WL may be turned off to avoid memory cell MC1from snapping back and to potentially reduce power requirements, forexample. In some examples, the voltage applied to word line WL and eachof bit lines BL0 and BL1 may be returned to the voltage V0 aftersensing.

FIG. 8A presents example timing diagrams (e.g., during a comparisonand/or a sensing operation), in accordance with a number of embodimentsof the present disclosure. FIG. 8B is an example of an operation, suchas a comparison and/or a sensing operation, being performed on a portionof a memory array 800 that may be a portion of memory array 100 ormemory array 400, in accordance with a number of embodiments of thepresent disclosure. The timing diagrams in FIG. 8A are in response toapplying a voltage to a bit line BL0 and a voltage to each of word linesWL0 to WL5 that cross bit line BL0 in FIG. 8B.

Memory cells MC0 to MC7 are respectively at crossings of word lines WL0to WL7 and bit line BL0. Memory cells MC0 to MC7 are respectivelycoupled to word lines WL0 to WL7 and commonly coupled to bit line BL0.Memory cells MC0 to MC7 may be similar to (e.g., the same as) memorycells 125. Memory cells MC1 to MC5 may be programmed to the positivestate 1 shown in FIGS. 2A and 2C and may respectively have thresholdvoltages Vt1 to Vt5. The threshold voltages Vt1 to Vt5 may be in thethreshold-voltage distribution 201-2 shown in FIG. 2A, for example. Insome examples, memory cells MC0, MC6, and MC7 may be programmed topositive state 0 shown in FIGS. 2A and 2B and may respectively havethreshold voltages Vt0, Vt6, and Vt7. The threshold voltages Vt0, Vt6,and Vt7 may be in the threshold-voltage distribution 200-2 shown in FIG.2A, for example.

Sensing circuitries 830-0 to 830-7 are respectively coupled to wordlines WL0 to WL7. For example, each of sensing circuitries 830-0 to830-7 may be similar to (e.g., the same as) the sensing circuitrydescribed previously in conjunction with FIG. 5 and/or FIG. 6. A wordline driver, such word line driver 550 or 650, is coupled to eachsensing circuitry 830 and each word line WL, as described previously,and a bit line driver, such as bit line driver 552 or 652, may becoupled to each bit line BL, as described previously. For example, thesetup described in conjunction with FIG. 5 or FIG. 6 may be used witheach bit line/word line combination in FIG. 8B.

The word line voltage signals VWL1 to VWL5 in FIG. 8A respectivelyrepresent the instantaneous word line voltage of word lines WL1 to WL5.A bit line voltage signal VBL0 represents the instantaneous bit linevoltage of bit line BL0. The voltage signals IPULS11 to IPULS15 in FIG.8A are the output voltage signals of sensing circuitries 830-1 to 830-5.The current signals IMC1 to IMC5 in FIG. 8A respectively represent theinstantaneous current flows through memory cells MC1 to MC5.

Initially, word lines WL0 to WL7 and bit line BL0 are at voltage V0, sothe voltage differential between bit line BL0 and word lines WL0 to WL7,and thus applied to memory cells MC0 to MC7, is initially about 0 volt.Voltage V1 is then applied to each of word lines WL0 to WL7 concurrently(e.g. in parallel). The example of FIG. 8A focuses on the behavior ofword lines WL1 to WL5 respectively coupled to memory cells MC1 to MC5and the snapback behavior of memory cells MC1 to MC5.

The word line voltage signals VWL1 to VWL5 decreases from the initialvoltage V0 to the voltage V1 in response to applying V1 to word linesWL1 to WL5. Although not shown in FIG. 8A, the voltages of word linesWL0, WL6, and WL7 may also decrease from the initial voltage V0 to thevoltage V1 in response to applying voltage V1 to word lines WL0, WL6,and WL7.

Voltage V2 is applied to bit line BL0 (e.g., after applying voltage V1to word lines WL1 to WL7). However, the present disclosure is notlimited to applying the voltage V2 after applying the voltage V1. Forexample, the voltages V1 and V2 might be applied at the same time orvoltage V2 might be applied before voltage V1. In some examples, voltageV2 may be a variable voltage of increasing magnitude, such as a rampvoltage of increasing magnitude or a series of increasing voltage pulsesof increasing magnitude. For example, voltage V2 may have an initialvalue equal to the voltage V1.

The voltage differential VDM1 between bit line BL0 and each of wordlines WL0 to WL7, and thus applied to memory cells MC0 to MC7, isVDM1=V2−V1. For example, FIGS. 8A and 8B depict a (e.g.,pseudo-parallel) sensing scheme, where a sensing voltage differential isapplied concurrently to memory cells MC0 to MC7. Similar timing diagramsmay depict applying the negative voltage differential VDM2 (FIG. 2A) tomemory cells MC0 to MC7. For examples in which voltage V2 may be avariable voltage, the voltage differential VDM1 may be a variablevoltage differential of increasing magnitude, such as a ramp voltagedifferential of increasing magnitude or a series of differential voltagepulses of increasing magnitude (e.g., having a starting voltage of zerovolts). For example, the voltage differential VDM1 may be increased(e.g., continuously in the case of a ramp voltage differential) fromzero volts until it is greater than the threshold voltage Vt4 of memorycell MC4, the memory cell with highest threshold voltage of memory cellsMC1 to MC5, and less than threshold voltages Vt0, Vt6, and Vt7respectively of memory cells MC0, MC6, and MC7.

The voltage differential VDM1 corresponds to an input state 0, forexample. The threshold voltages Vt1 to Vt5 respectively of memory cellsMC1 to MC5 are less than voltage differential VDM1 and snap back inresponse to the voltage differential VDM1. The threshold voltages Vt0,Vt6, and Vt7 respectively of memory cells MC0, MC6, and MC7 are greaterthan voltage differential VDM1 and do not snap back in response tovoltage differential VDM1.

Bit line voltage signal VBL0 increases from voltage V0 to voltage V3 inresponse to applying voltage V2 to bit line BL0 while word lines WL1 toWL5 are at voltage V1. Memory cell MC2 snaps back in response to the bitline voltage signal VBL0 reaching the voltage V3 while word lines WL1 toWL5 are at voltage V1. For example, the threshold voltage Vt2 of memorycell MC2 is Vt2=V3−V1. In response to memory cell MC2 snapping back, bitline voltage signal VBL0 decreases from voltage V3 to a voltage V4; theword line voltage signal VWL2 increases from voltage V1 to a voltage V9while the voltage signal VBL0 decreases from voltage V3 to voltage V4;and the current signal IMC2 increases from the current I0 to a currentI2. The increase in the current signal IMC2 causes the bit line voltagesignal VBL0 to start to increase from voltage V4 to a voltage V11, forexample.

The voltage signals IPULS11 to IPULS15 may remain at initial presetvoltage V6, while the word line voltage signals VWL1 to VWL5 decrease tothe voltage V1 and while the bit line voltage signal VBL0 increases tothe voltage V3.

The voltage signal IPULS12 decreases from the voltage V6 to voltage V7in response to sensing circuitry 830-2 detecting the increase in thevoltage of voltage signal VWL2. The sensing circuitry 830-2 acts to turnoff the current to word line WL2 in response to voltage signal IPULS12decreasing to voltage level V7, and thus memory cell MC2 snapping back.For example, sensing circuitry 830-2 acts to decouple word line WL2 froma voltage node (e.g., causing word line WL2 to float). For example,turning off the current to word line WL2 acts to prevent any futuresnapbacks of memory cell MC2 and may act to reduce power consumption.

In some examples, the threshold voltage of memory cell MC2 is less thanthe threshold voltages of memory cells MC1 and MC3 to MC5. For example,the threshold voltage of memory cell MC2 is reached before the thresholdvoltages of memory cells MC1 and MC3 to MC5 are reached, and thus memorycell MC2 snaps back before memory cells MC1 and MC3 to MC5.

In some examples, word line voltage signal VWL2 increases from voltageV9 to a voltage V12 and current signal IMC2 decreases while bit linevoltage signal VBL0 increases from voltage V4 to a voltage V11.

Memory cell MC3 snaps back in response to the bit line voltage signalVBL0 reaching the voltage V11 while word lines WL1 and WL3 to WL5 are atvoltage V1 and while word line WL2 is at voltage V12. For example, thethreshold voltage Vt3 of memory cell MC3 is Vt3=V11−V1.

In response to memory cell MC3 snapping back, bit line voltage signalVBL0 decreases from voltage V11 to a voltage V13; the word line voltagesignal VWL3 increases from voltage V1 to a voltage V14 while the bitline voltage signal VBL0 decreases from voltage V11 to voltage V13; andthe current signal IMC3 increases from the current JO to a current I3.For example, the increase to current I3 may cause the bit line voltagesignal VBL0 to start to increase from voltage V13 to a voltage V24. Insome examples, the current signal IMC2 is cut off and goes to current JOin response to memory cell MC3 snapping back.

The voltage signals IPULS11, IPULS13, IPULS14, and IPULS15 remain atvoltage V6 and voltage signal IPULS12 remains at voltage V7 (e.g., thecurrent to word line WL2 is off) while the bit line voltage signal VBL0increases to the voltage V11 and subsequently decreases to voltage V13,memory cell MC3 snaps back, and the word line voltage signal VWL2increases to voltage V12.

The voltage signal IPULS13 decreases from the voltage V6 to voltage V7in response to sensing circuitry 830-3 detecting the increase in thevoltage of word line voltage signal VWL3. The sensing circuitry 830-3acts to turn off the current to word line WL3 in response to voltagesignal IPULS13 decreasing to voltage level V7, and thus memory cell MC3snapping back. For example, sensing circuitry 830-3 acts to decoupleword line WL3 from a voltage node (e.g., causing word line WL3 tofloat). For example, turning off the current to word line WL3 acts toprevent any future snapbacks of memory cell MC3 and may act to reducepower consumption.

In some examples, the threshold voltage of memory cell MC3 is less thanthe threshold voltages of memory cells MC1, MC4, and MC5. For example,the threshold voltage of memory cell MC3 is reached before the thresholdvoltages of memory cells MC1, MC4, and MC5 are reached, and thus memorycell MC3 snaps back before memory cells MC1, MC4, and MC5.

In some examples, word line voltage signal VWL3 increases from voltageV14 to voltage V12 and current signal IMC3 decreases while bit linevoltage signal VBL0 increases from voltage V13 to a voltage V24.

Memory cell MC1 snaps back to its conductive state in response to thebit line voltage signal VBL0 reaching the voltage V24 while word linesWL1, WL4, and WL5 are at voltage V1, word line WL2 is at voltage V12,and word line WL3 is increasing to or at voltage V12. For example, thethreshold voltage Vt1 of memory cell MC1 may be Vt1=V24−V1.

In response to memory cell MC1 snapping back, bit line voltage signalVBL0 decreases from voltage V24 to a voltage V15; the word line voltagesignal VWL1 increases from voltage V1 to a voltage V16 while the bitline voltage signal VBL0 decreases from voltage V24 to voltage V15; andthe current signal IMC1 increases from the current I0 to a current I4.For example, the increase to current I4 causes the bit line voltagesignal VBL0 to start to increase from voltage V15 to a voltage V17. Insome examples, the current signal IMC3 is cut off and goes to current I0in response to memory cell MC1 snapping back.

The voltage signals IPULS11, IPULS14, and IPULS15 remain at voltage V6and voltage signals IPULS12 and IPULS13 remain at voltage V7 (e.g., thecurrent to word lines WL2 and WL3 is off) while the bit line voltagesignal VBL0 increases to the voltage V24 and subsequently decreases tovoltage V15, memory cell MC1 snaps back, and the word line voltagesignal VWL3 increases to voltage V12.

The voltage signal IPULS11 decreases from the voltage V6 to voltage V7in response to sensing circuitry 830-1 detecting the increase in thevoltage of word line voltage signal VWL1. The sensing circuitry 830-1acts to turn off the current to word line WL1 in response to voltagesignal IPULS11 decreasing to voltage level V7, and thus memory cell MC1snapping back. For example, sensing circuitry 830-1 acts to decoupleword line WL1 from a voltage node (e.g., causing word line WL1 tofloat). For example, turning off the current to word line WL1 acts toprevent any future snapbacks of memory cell MC1 and may act to reducepower consumption.

In some examples, the threshold voltage of memory cell MC1 is less thanthe threshold voltages of memory cells MC4 and MC5. For example, thethreshold voltage of memory cell MC1 is reached before the thresholdvoltages of memory cells MC4 and MC5 are reached, and thus memory cellMC1 snaps back before memory cells MC4 and MC5.

In some examples, word line voltage signal VWL1 increases from voltageV16 to voltage V12 and current signal IMC1 decreases while bit linevoltage signal VBL0 increases from voltage V15 to voltage V17.

Memory cell MC5 snaps back in response to the bit line voltage signalVBL0 reaching the voltage V17 while word lines WL4 and WL5 are atvoltage V1 and while word lines WL1, WL2, and WL3 are at voltage V12.For example, the threshold voltage Vt5 of memory cell MC5 is Vt5=V17−V1.

In response to memory cell MC5 snapping back, bit line voltage signalVBL0 decreases from voltage V17 to a voltage V18; the word line voltagesignal VWL5 increases from voltage V1 to a voltage V19 while the bitline voltage signal VBL0 decreases from voltage V17 to voltage V18; andthe current signal IMC5 increases from the current JO to a current I5.For example, the increase to current I5 causes the bit line voltagesignal VBL0 to start to increase from voltage V18 to a voltage V20. Insome examples, the current signal IMC1 is cut off and goes to current JOin response to memory cell MC5 snapping back.

The voltage signals IPULS14 and IPULS15 remain at voltage V6 and voltagesignals IPULS11, IPULS12, and IPULS13 remain at voltage V7 (e.g., thecurrent to word lines WL1, WL2, and WL3 is off) while the bit linevoltage signal VBL0 increases to the voltage V17 and subsequentlydecreases to voltage V18, memory cell MC5 snaps back, and the word linevoltage signal VWL1 increases to voltage V12.

The voltage signal IPULS15 decreases from the voltage V6 to voltage V7in response to sensing circuitry 830-5 detecting the increase in thevoltage of word line voltage signal VWL5. The sensing circuitry 830-5acts to turn off the current to word line WL5 in response to voltagesignal IPULS15 decreasing to voltage level V7, and thus memory cell MC5snapping back. For example, sensing circuitry 830-5 acts to decoupleword line WL5 from a voltage node (e.g., causing word line WL5 tofloat). For example, turning off the current to word line WL5 acts toprevent any future snapbacks of memory cell MC5 and may act to reducepower consumption.

In some examples, the threshold voltage of memory cell MC5 is less thanthe threshold voltage of memory cell MC4. For example, the thresholdvoltage of memory cell MC5 is reached before the threshold voltage ofmemory cell MC4 is reached, and thus memory cell MC5 snaps back beforememory cell MC4.

In some examples, word line voltage signal VWL5 increases from voltageV19 to voltage V12 and current signal IMC5 decreases while bit linevoltage signal VBL0 increases from voltage V18 to a voltage V20.

Memory cell MC4 snaps back to its conductive state in response to thebit line voltage signal VBL0 reaching the voltage V20 while word lineWL4 is at voltage V1 and while word lines WL1, WL2, WL3, and WL5 are atvoltage V12. For example, the threshold voltage Vt4 of memory cell MC4is Vt4=V20−V1.

In response to memory cell MC4 snapping back, bit line voltage signalVBL0 decreases from voltage V20 to a voltage V21; the word line voltagesignal VWL4 increases from voltage V1 to a voltage V22 while the bitline voltage signal VBL0 decreases from voltage V20 to voltage V21; andthe current signal IMC4 increases from the current JO to a current I6.For example, the increase to current I6 may cause the bit line voltagesignal VBL0 to start to increase from voltage V21 to voltage V2. In someexamples, the current signal IMC5 is cut off and goes to current JO inresponse to memory cell MC4 snapping back.

The voltage signal IPULS14 remains at voltage V6 and voltage signalsIPULS11, IPULS12, IPULS13, and IPULS15 remain at voltage V7 (e.g., thecurrent to word lines WL1, WL2, WL3, and WL5 is off) while the bit linevoltage signal VBL0 increases to the voltage V20 and subsequentlydecreases to voltage V21, memory cell MC4 snaps back, and the word linevoltage signal VWL5 increases to voltage V12.

The voltage signal IPULS14 decreases from the voltage V6 to voltage V7in response to sensing circuitry 830-4 detecting the increase in thevoltage of word line voltage signal VWL4. The sensing circuitry 830-4acts to turn off the current to word line WL4 in response to voltagesignal IPULS14 decreasing to voltage level V7, and thus memory cell MC4snapping back. For example, sensing circuitry 830-4 acts to decoupleword line WL4 from a voltage node (e.g., causing word line WL4 tofloat). For example, turning off the current to word line WL4 acts toprevent any future snapbacks of memory cell MC4 and may act to reducepower consumption.

While bit line voltage signal VBL0 increases from voltage V21 to voltageV2, the word line voltage signal VWL4 increases from voltage V22 tovoltage V12 and current signal IMC4 decreases from current I6 to currentJO.

In some examples, the voltages on word lines WL1 to WL5 go to thevoltage V12 while the voltage on bit line BL0 goes to voltage V2 suchthat the differences between the voltages on word lines WL1 to WL5 andbit line BL0 are V2 V12, which is less than the threshold voltages ofmemory cells MC1 to MC5. Although the example of FIG. 8A shows that thevoltages on word lines WL1 to WL5 go to the common voltage V12, thepresent disclosure is not so limited, and the voltages on word lines WL1to WL5 may go voltages that are different than each other such that thedifferences between those voltages on word lines WL1 to WL5 and thevoltage on bit line BL0 are less than the threshold voltages of memorycells MC1 to MC5.

Although not shown in FIG. 8A, voltage signals (e.g., corresponding toinstantaneous voltages) on word lines WL0, WL6, and WL7 may decreasefrom the voltage V0 to V1 in response to applying the voltage V1 to wordlines WL0, WL6, and WL7 and may remain at the V1 while the bit linevoltage signal VBL0 may behave as shown in the example of FIG. 8A, inthat the threshold voltages of memory cells MC0, MC6, and MC7respectively at the crossings of word lines WL0, WL6, and WL7 and bitline BL0 may be greater than the voltage differential VDM1 and thus donot snap back. For example, the sensing scheme may indicate that memorycells MC0, MC6, and MC7 are in positive state 0, in that these memorycells do not snap back, and the sensing scheme may indicate that memorycells MC1 to MC5 are in state 1, in that these memory cells do snapback. In addition, the memory cells MC0, MC6, and MC7 not snapping backmay indicate a match between the input state and the state stored bymemory cells MC0, MC6, and MC7, and memory cells MC1 to MC5 snappingback may indicate a mismatch between the input state and the statestored by memory cells MC1 to MC5. In some examples, the voltage signalson all word lines WL0 to WL7 may decrease from the voltage V0 to V1 inresponse to applying the voltage V1 to word lines WL0 to WL7 and mayremain at the V1 while the bit line voltage signal VBL0 may behave asshown in the example of FIG. 8A, in that the threshold voltages ofmemory cells MC0 to MC7 respectively at the crossings of word lines WL0to WL7 and bit line BL0 may be greater than the voltage differentialVDM1 and thus do not snap back, indicative of a match between the inputvalue and the stored value. Note that FIG. 8A refers to the first phaseshown in FIG. 4. Similar considerations to those depicted in FIG. 8A maybe applied during the second phase of FIG. 4, for example, with thevoltages depicted in FIG. 8A reversed.

In the example of the parallel sensing previously described inconjunction with FIG. 8A, the memory cells MC2, MC3, MC1, MC5, and MC4are selected one at a time by their respective snapback events. Forexample, the memory cells MC2, MC3, MC1, MC5, and MC4 are selected oneat time in order as a result of their respective threshold voltages(e.g., starting with memory cell MC2 having the lowest threshold voltage(e.g., and/or lowest threshold delay) and ending with memory cell MC4having the highest threshold voltage (e.g., and/or highest thresholddelay)). This can prevent more than one cell from snapping back at atime. Detection circuitry (e.g. sensing circuitry) detects the snapbackof a respective cell, turns that cell off, and allows the next cell(e.g., with the next highest threshold voltage) to be snapped back. Thethreshold delay, for example, is the time it takes for a memory cell tosnap back in response to an applied voltage. The parallel sensing in theexample of FIG. 8A may act to amortize the individual threshold delaysof memory cells MC1 to MC5 among memory cells MC1 to MC5.

The increase in the voltages of the word line signals VWL1 to VWL5 inresponse to the respective memory cells MC1 to MC5 snapping back are,for example, a consequence of the current limiting by the detectioncircuitry. For example, the current in the respective word lines WL1 toWL5 may increase as a result of the respective memory cells MC1 to MC5snapping back. When the current in a word line corresponding to one ofthe memory cells reaches a particular level, for example, the voltage ofthe word line increases as a result of the current limiting.

FIG. 9A illustrates an example of a data store (e.g., a vector store)operation in accordance with a number of embodiments of the presentdisclosure. For example, an input vector may be stored to a portion of amemory array 900 that may be a portion of memory array 100 or memoryarray 400. The input vector may be written to memory cells MC0 to MC7commonly coupled to word line WL4 and respectively coupled to bit linesBL0 to BL7. For example, bit0 to bit7 of the input vector may berespectively written to memory cells MC0 to MC7 to form a stored vector.

Memory cells MC0 to MC7 may be similar to (e.g., the same as) memorycells 125. Sensing circuitries 930-0 to 930-7 are respectively coupledto bit lines BL0 to BL7. Each of the sensing circuitries 930-0 to 930-7may be similar to sensing circuitries previously described inconjunction with FIG. 5 and/or FIG. 6. For example, the setups shown inFIG. 5 or 6 may be used with memory array 900, but with the word lineand the bit line interchanged.

To write a positive state 1 in a memory cell initially in a positivestate 0 (e.g., corresponding to threshold-voltage distribution 200-2),such as shown in FIG. 2A, a positive voltage differential VWRITE0 may beapplied between the bit line and the word line, and thus to (e.g.,across) that memory cell. For example, voltage differential VWRITE0 maybe greater than the threshold voltage of the memory cell (e.g., greaterthan the threshold voltages in the threshold-voltage distribution 200-2corresponding to positive state 0), as shown in FIG. 2A.

To write a negative state 0 in a memory cell initially in a negativestate 1 (e.g., corresponding to a threshold-voltage distribution 201-1),such as shown in FIG. 2A, a negative voltage differential VWRITE1 may beapplied between the bit line and the word line, and thus to that memorycell. For example, voltage differential VWRITE1 may be greater in anegative sense than the threshold voltage of the memory cell (e.g.,greater in a negative sense than the threshold voltages inthreshold-voltage distribution 201-1 corresponding to negative state 0),as shown in FIG. 2A.

FIG. 9B illustrates examples of signals, such as write voltages, inaccordance with a number of embodiments of the present disclosure. Forexample, voltage differential VWRITE0 is VWRITE0=VBL0−VWL0, where VBL0is the bit line voltage applied to the bit line coupled to the memorycell to be written (e.g., programmed) to positive state 1 from positivestate 0 and VWL0 is the word line voltage applied to the word linecoupled to that memory cell. Voltage differential VWRITE1 isVWRITE1=VBL1−VWL1, for example, where VBL1 is the bit line voltageapplied to the bit line coupled to the memory cell to be written (e.g.,programmed) to negative state 0 from negative state 1 and VWL1 is theword line voltage applied to the word line coupled to that memory cell.

In the example of FIG. 9B, a signal, such as the word line voltage VWL0,goes to a voltage VLOW (e.g., to about 0 volt) from an intermediatevoltage V0 and may, for example, stay at VLOW, while a signal (e.g., aseries of voltage pulses VBLPULS) are applied to the bit line coupled tothe memory cell to be written. For example, each voltage pulse VBLPULShas a magnitude of VHIGH V0. For example, this means that a series ofdifferential voltage pulses VWRITE0 of magnitude VHIGH−VLOW are appliedto the memory cells to be written to positive state 1 from positivestate 0. This may be accomplished, for example, by applying the seriesof differential voltage pulses VWRITE0 between the word lines and bitlines between which those memory cells are coupled. In some examples,the differential voltage pulses VWRITE0 are applied to the memory cellsto be written to positive state 1 during a first phase, and an inhibitvoltage differential (e.g., about zero volt), where VBL0 and VWL0 may beat voltage V0, is applied during a second phase. For example, thewriting during the first phase may be performed concurrently (e.g., inparallel, such as to memory cells respectively coupled to different bitlines and commonly coupled to one word line) to the memory cells thatare to store positive state 0.

In some examples, a pulse (e.g., each pulse) VWRITE0 causes the memorycell to snap back. In some examples, the sensing circuitry coupled tothe bit line coupled to the memory cell may act to cause current to thebit line to be turned off in response to each time the memory cell snapsback. For example, sensing circuitry may act to decouple bit line from avoltage node (e.g., causing bit line to float) in response to each timethe memory cell snaps back.

Each time the memory cell snaps back, a pulse of current (e.g., acurrent transient), such as ICURPULS in FIG. 9C, flows (e.g., pulse)through the memory cell. For example, each current pulse ICURPULS maydeliver (e.g., impart) energy to the memory cell during a time durationtime0 shown in FIG. 9C. In some examples, the number of pulses VWRITE0may be such that the energy delivered to the memory cell by thecorresponding current pulses ICURPULS may be sufficient to cause thememory cell to go to positive state 1 from positive state 0. In someexamples, the differential write pulses VWRITE0 may be applied until thememory cell is programmed to positive state 1, where each time thememory cell snaps back, it moves toward positive state 1.

In some examples, each snapback event, such as each time a memory cellsnaps back (e.g., each time a memory cell goes from a high-impedancestate to a lower impedance state), the state of the memory cell may movetoward the positive state 1. For example, the state of a memory cell maytend toward state 1 as the memory cell snaps back. In some examples, thenumber of times a memory cell might need to snap back to go from state 0to state 1 might be estimated (e.g., based on a number of snapbacks itmight take for a sample of memory cells to go from state 0 to state 1).Note, for example, that as the memory cell goes toward state 1 fromstate 0, its threshold voltage may decrease. In some examples, a memorycell might be sensed (e.g., as described previously) after a certainnumber of snapbacks to determine whether the memory cell is programmed.

In another example, both the bit line voltage VBL0 and the word linevoltage VWL0 may be may be constant (e.g., to within routine variationsin the voltages VBL0 and VWL0), meaning that the voltage differentialVWRITE0 may be constant. The constant voltage differential VWRITE0 maybe applied to the memory cell for a certain time and may cause thememory cell to snapback, resulting in a constant current ICUR (e.g., towithin routine variations in the current) through the memory cell, asshown in FIG. 9C. The constant voltage differential VWRITE0 may beapplied to the memory cell until the constant current ICUR deliverssufficient energy (e.g., about the same as that delivered by the numberof current pulses ICURPULS) to the memory cell so that the memory cellgoes to positive state 1. For example, the time duration of the constantcurrent ICUR such that the memory cell goes to positive state 1 may be atime1, as shown in FIG. 9C.

In the example of FIG. 9B, the bit line voltage VBL1 goes to the voltageVLOW and, for example, stays at VLOW, while a series of voltage pulsesVWLPULS are applied to the word line. For example, each voltage pulseVWLPULS has a magnitude of VHIGH−V0. For example, this means that aseries of differential voltage pulses VWRITE1 of a magnitude VHIGH−VLOWare applied to the memory cells. In some examples, the differentialvoltage pulses VWRITE1 (e.g., having a polarity opposite to thedifferential voltage pulses VWRITE0) are applied to memory cells to beprogrammed to negative state 0 from negative state 1 during the secondphase, and an inhibit voltage differential (e.g., about zero volt),where VBL1 and VWL1 may be a voltage V0, is applied during the firstphase. For example, the writing during the second phase may be performedconcurrently (e.g., in parallel, such as to memory cells respectivelycoupled to different bit lines and commonly coupled to one word line) tothe memory cells that are to store negative state 0. For example, thewriting depicted in FIGS. 9A and 9B may be referred to as apseudo-parallel store to memory cells respectively coupled to differentbit lines and commonly coupled to one word line. However, the presentdisclosure is not limited to applying the differential voltage pulsesVWRITE0 and the differential voltage pulses VWRITE1 in different phases,for example.

In some examples, a pulse (e.g., each pulse) VWRITE1 causes the memorycell to snapback. In some examples, the sensing circuitry coupled to thebit line coupled to the memory cell may act to cause current to the bitline to be turned off in response to each time the memory cell snapsback.

Each time the memory cell snaps back a pulse of current (e.g., a currenttransient) similar to ICURPULS in FIG. 9C, may flow through the memorycell. In some examples, the number of pulses VWRITE1 may be such thatthe energy delivered to the memory cell by the corresponding currentpulses may be sufficient to cause the memory cell to go to negativestate 0 from negative state 1. For example, the state of a memory cellmay tend toward state 0 in response to a number of times the memory cellsnaps back. Note, for example, that as the memory cell goes towardnegative state 0 from negative state 1, its threshold voltage maydecrease in a negative sense. The sensing circuitry coupled to the bitline coupled to the memory cell that snaps back may output a feedbacksignal that may act to turn off the current to that bit line in responseto that sensing circuitry detecting the snapback (e.g., in a mannersimilar to that described previously for turning off the word linecurrent in conjunction with FIGS. 6, 7A, and 7B). In some examples, thedifferential write pulses VWRITE1 may be applied until the memory cellis programmed to negative state 0, where each time the memory cell snapsback, it moves toward negative state 0.

In some examples, the memory cells to be written may be sensed beforewriting (e.g., using the sensing schemes described previously) todetermine whether the memory cells might need to be written. Forexample, memory cells already in positive state 1 or negative state 0,as indicated by the sensing scheme, might not need to be written.

In some examples, programming a memory cell from a positive state 0 to apositive state 1 or from a negative state 1 to a negative state 0, maycause the magnitude of threshold voltage of the memory cell to decrease.

FIG. 10A illustrates another example of a data store operation, inaccordance with a number of embodiments of the present disclosure. Forexample, data may be written to memory cells MC0 to MC3 commonly coupledto a bit line BL and respectively coupled to word lines WL0 to WL3.Sensing circuitries 1030-0 to 1030-3 may be respectively coupled to wordlines WL0 to WL3. For example, sensing circuitries 1030-0 to 1030-3 maybe similar to (e.g., the same as) the sensing circuitry describedpreviously in conjunction with FIG. 5 and/or FIG. 6. A word line driver,such word line driver 550 or 650, is coupled to each sensing circuitry1030 and each word line WL, as described previously, and a bit linedriver, such as bit line driver 552 or 652, is coupled to bit line BL,as described previously. For example, the setup described in conjunctionwith FIG. 5 or FIG. 6 may be used with each bit line/word linecombination in FIG. 10A.

In the example of FIG. 10A, it is desired to program memory cells MC1 toMC3 from the positive state 0 in FIG. 2A to the positive state 1 in FIG.2A. FIG. 10B presents example timing diagrams (e.g., during a data storeoperation) in accordance with a number of embodiments of the presentdisclosure. For example, the timing diagrams may correspond to thewriting (e.g., programming) in FIG. 10A. Timing diagrams similar tothose in FIG. 10B may correspond to programming memory cells MC1 to MC3from the negative state 1 in FIG. 2A to the negative state 0 in FIG. 2A.

The word line voltage signals VWL0 to VWL3 in FIG. 10B may respectivelyrepresent the instantaneous word line voltage of word lines WL0 to WL3.A bit line voltage signal VBL may represent the instantaneous bit linevoltage of bit line BL. The voltage signals IPULS10 to IPULS13 in FIG.10B may respectively be the output voltage signals of sensingcircuitries 1030-0 to 1030-3. The current signals IMC0 to IMC3 in FIG.10B may respectively represent the instantaneous current flows throughmemory cells MC0 to MC3.

Initially, a signal, such as a voltage V0, is applied to word lines WL0to WL3 and bit line BL. In some examples, a sense voltage (e.g., pulse)VDM1=V2−V1 is applied to memory cells MC0 to MC3 to determine theircurrent states, where VDM1 is shown in FIG. 2A. For example, a signal,such as a voltage V1, is applied to word lines WL0 to WL3. The word linevoltage signals VWL0 to VWL3 decrease from the initial voltage V0 to thevoltage V1 in response to applying V1 to word lines WL0 to WL3.

Subsequently, a signal, that may include the sensing bit line voltagepulse VBLSENS and writing bit line voltage pulses VBLWRIT1 and VBLWRIT2,in FIG. 10A may be applied to bit line BL. For example, applying voltagepulse VBLSENS includes increasing the voltage on bit line BL from thevoltage V0 to voltage V2 so the voltage pulse VBLSENS has a magnitude ofV2-V0. For example, this results in applying the differential sensevoltage pulse VDM1=V2−V1 between bit line BL and each of word lines WL0to WL3, and thus to memory cells MC0 to MC3.

Bit line voltage signal VBL increases to voltage V3 in response toapplying voltage pulse VBLSENS to bit line BL while word lines WL1 toWL3 are at voltage V1. Memory cell MC0 snaps back in response to the bitline voltage signal VBL reaching the voltage V3 while word lines WL0 toWL3 are at voltage V1. For example, the threshold voltage Vt0 of memorycell MC0 is Vt0=V3−V1 that is less than VDM1. Snapping back of memorycell MC0 indicates that memory cell MC0 is in the positive state 0 anddoes not need to be written.

In response to memory cell MC0 snapping back, the bit line voltagesignal VBL decreases to a voltage V102; the word line voltage signalVWL0 increases from voltage V1 to a voltage V104; and the current signalIMC0 increases from current level I0 (about 0 amp) to a current level1101. The increase in the current signal IMC0 causes the bit linevoltage signal VBL to start to increase, for example, from voltage V102to voltage V2.

Sensing circuitry 1030-0 senses the increase in the voltage of word linevoltage signal VWL0, thereby identifying memory cell MC0 as the memorycell snapping back, and thus being at positive state 1. Voltage signalIPULS10 decreases from voltage V6 to voltage V7 in response to sensingcircuitry 1030-0 sensing the increase in the voltage of word line WL0,and thus memory cell MC0 snapping back. The sensing circuitry 1030-0acts to turn off the current to word line WL0 in response to voltagesignal IPULS10 decreasing to voltage level V7, and thus memory cell MC0snapping back. For example, sensing circuitry 1030-0 acts to decoupleword line WL0 from a voltage node (e.g., causing word line WL0 tofloat). The current signal IMC0 decreases to current level I0 fromcurrent level 1101 while bit line voltage signal VBL increases tovoltage V2.

The bit line voltage signal VBL increases from voltage V102 to voltageV2 without any additional snap backs. This indicates that memory cellsMC1 to MC3 are at the positive state 0 and may need to be written to thepositive state 1. The voltage pulse VBLSENS is then be removed from bitline BL so that the voltage on bit line BL is returned to voltage V0while word lines WL1 to WL3 are at voltage V1 and while word line WL0 isat voltage V104. The bit line voltage signal VBL then decreases to thevoltage V0 in response to removing the voltage pulse VBLSENS. The wordline voltage signal remains at voltage V104 while bit line voltagesignal VBL decreases to the voltage V0.

While the word line voltage signals VWL1 to VWL3 are at voltage V1, asignal pulse, such as the writing bit line voltage pulse VBLWRIT1 inFIG. 10A, is applied to bit line BL. For example, applying voltage pulseVBLWRIT1 includes increasing the voltage on bit line BL from the voltageV0 to voltage V110 (e.g., about 7.0 volts), so the voltage pulseVBLWRIT1 has a magnitude of V110-V0. For example, this results inapplying a signal pulse, such as a differential write voltage pulseVWRITE01=V110−V1, between bit line BL and each of word lines WL0 to WL3,and thus to memory cells MC0 to MC3.

Bit line voltage signal VBL increases to a voltage V112 from voltage V0in response to applying voltage pulse VBLWRIT1 to bit line BL while wordlines WL1 to WL3 are at voltage V1 and word line WL0 is at voltage V104that inhibits memory cell MC0 from changing state in response to voltagepulse VBLWRIT1. Memory cell MC1 snaps back in response to the bit linevoltage signal VBL reaching the voltage V112 while word lines WL1 to WL3are at voltage V1. For example, the threshold voltage Vt1 of memory cellMC1 is Vt1=V112−V1 that is less than VWRITE01.

In response to memory cell MC1 snapping back, the bit line voltagesignal VBL decreases to a voltage V114; word line voltage signal VWL1increases from voltage V1 to a voltage V116; and the current signal IMC1increases from current level I0 to a current level 1102 (e.g., toproduce pulse of current, such as a current pulse, through memory cellMC1).

The sensing circuitry 1030-1 senses the increase in the voltage of wordline voltage signal VWL1. Voltage signal IPULS11 decreases from voltageV6 to voltage V7 in response to sensing circuitry 1030-1 sensing theincrease in the voltage of word line WL1, and thus memory cell MC1snapping back. The sensing circuitry 1030-1 acts to turn off the currentto word line WL1 in response to voltage signal IPULS11 decreasing tovoltage V7, and thus memory cell MC1 snapping back. For example, sensingcircuitry 1030-1 acts to decouple word line WL1 from a voltage node(e.g., causing word line WL1 to float). The current signal IMC1decreases to current level I0 from current level 1102 while bit linevoltage signal VBL increases to voltage V120.

The voltage on word line WL0 remains at voltage V104; the voltage signalVWL1 increases to voltage V116; and the voltages on word lines WL2 andWL3 remain at voltage V1 while bit line voltage signal VBL increases tovoltage V120. Memory cell MC2 snaps back in response to bit line voltagesignal VBL reaching voltage V120. For example, the threshold voltage Vt2of memory cell MC2 may be Vt2=V120−V1 that is less than VWRITE01.

In response to memory cell MC2 snapping back, the bit line voltagesignal VBL decreases to a voltage V122; word line voltage signal VWL2increases from voltage V1 to voltage V116; and the current signal IMC2increases from current level I0 to a current level 1103 (e.g., toproduce pulse of current, such as a current pulse, through memory cellMC2).

Sensing circuitry 1030-2 senses the increase in the voltage of word linevoltage signal VWL2. Voltage signal IPULS12 decreases from voltage V6 tovoltage V7 in response to sensing circuitry 1030-2 sensing the increasein the voltage of word line WL2, and thus memory cell MC2 snapping back.The sensing circuitry 1030-2 acts to turn off the current to word lineWL2 in response to voltage signal IPULS12 decreasing to voltage V7, andthus memory cell MC2 snapping back. For example, sensing circuitry1030-2 acts to decouple word line WL2 from a voltage node (e.g., causingword line WL2 to float). The current signal IMC2 decreases to currentlevel I0 from current level 1103 while bit line voltage signal VBLincreases to voltage V126.

The voltage on word line WL0 remains at voltage V104; the voltage onword line WL1 remains at voltage V116; the voltage signal VWL2 increasesto voltage V116; and the voltage on word line WL3 remains at voltage V1while bit line voltage signal VBL increases to voltage V126. Memory cellMC3 snaps back in response to bit line voltage signal VBL reachingvoltage V126. For example, the threshold voltage Vt3 of memory cell MC3is Vt3=V126−V1 that is less than VWRITE01.

In response to memory cell MC3 snapping back, the bit line voltagesignal VBL decreases to a voltage V128; word line voltage signal VWL3increases from voltage V1 to voltage V116; and the current signal IMC3increases from current level I0 to a current level 1104 (e.g., toproduce pulse of current, such as a current pulse, through memory cellMC3).

Sensing circuitry 1030-3 senses the increase in the voltage of word linevoltage signal VWL3. Voltage signal IPULS13 decreases from voltage V6 tovoltage V7 in response to sensing circuitry 1030-3 sensing the increasein the voltage of word line WL3, and thus memory cell MC3 snapping back.The sensing circuitry 1030-3 acts to turn off the current to word lineWL3 in response to voltage signal IPULS13 decreasing to voltage V7, andthus memory cell MC3 snapping back. For example, sensing circuitry1030-3 acts to decouple word line WL3 from a voltage node (e.g., causingword line WL3 to float). The current signal IMC3 decreases to currentlevel I0 from current level 1104 while bit line voltage signal VBLincreases to voltage V110.

After the bit line voltage signal VBL reaches voltage V110, the writingassociated with applying the write voltage pulse VWRITE01 to memorycells MC1 to MC3 is completed, and the voltage pulse VBLWRIT1 is removedfrom bit line BL, so that the voltage applied to bit line BL is returnedto voltage V0. For example, memory cells MC1 to MC3 may move towardstate 1 in response to voltage pulse VBLWRIT1, and may be in anintermediate state between state 0 and state 1. In some examples, thesense operation described in conjunction with memory cell MC0 may beperformed after the writing associated with applying the differentialwrite voltage pulse VWRITE01 to memory cells MC1 to MC3 is completed.

In the example of FIG. 10B after the bit line voltage signal VBL reachesvoltage V110, the voltage on word line WL0 is decreased from voltageV104 to voltage V1; the voltages on word lines WL1 to WL3 are decreasedfrom voltage V116 to voltage V1; and the voltages of sensing circuitries1030-0 to 1030-3 are reset to voltage V6. Although the example of FIG.10B shows the voltage signals VWL1 to VWL3 increasing to the samevoltage V116 in response to memory cells MC1 to MC3 respectivelysnapping back, the present disclosure is not so limited. In otherexamples, the voltage signals VWL1 to VWL3 may increase to differentvoltages in response to memory cells MC1 to MC3 respectively snappingback.

Subsequently, while the voltages on word lines WL1 to WL3 are once againat voltage V1, a signal pulse, such as the writing bit line voltagepulse VBLWRIT2 in FIG. 10A, is applied to bit line BL. For example,applying voltage pulse VBLWRIT2 includes increasing the voltage on bitline BL from the voltage V0 to voltage V110, so the voltage pulseVBLWRIT2 has a magnitude of V110−V0. For example, this results inapplying a signal pulse, such as a differential write voltage pulseVWRITE02=V110−V1, between bit line BL and each of word lines WL1 to WL3,and thus to memory cells MC1 to MC3. Note, for example, that memory cellMC0 is already at positive state 1 and may be inhibited from writing,such as by applying a voltage to word line WL0 so that the voltagedifferential applied to memory cell MC0 is less than the thresholdvoltage of memory cell MC0.

In some examples, the bit line voltage signal VBL, the word line voltagesignals VWL1 to VWL3, the output voltage signals respectively of sensingcircuitries 1030-1 to 1030-3, and the current signals IMC1 to IMC3 mayrespond to applying voltage V1 to word lines WL1 to WL3 and applyingvoltage pulse VBLWRIT2 to bit line BL, and thus applying differentialwrite voltage pulse VWRITE02 to memory cells MC1 to MC3, as previouslydescribed in response to applying voltage V1 to word lines WL1 to WL3and applying voltage pulse VBLWRIT1 to bit line BL, and thus applyingdifferential write voltage pulse VWRITE01 to memory cells MC1 to MC3.

For example, memory cells MC1 to MC3 snap back in response to applyingdifferential write voltage pulse VWRITE02 to memory cells MC1 to MC3.The word line voltage signals VWL1 to VWL3, for example, respectivelyincrease to voltage V116 from voltage V1 in response to memory cells MC1to MC3 snapping back. Current signals IMC1 to IMC3, for example,respectively increase to current levels 1102, 1103, and 1104 fromcurrent level I0 snapping back to form current pulses respectivelythrough memory cells MC1 to MC3. For example, sensing circuitries 1030-1to 1030-3 respectively turn off the current to word lines WL1 to WL3 inresponse to memory cells MC1 to MC3 respectively snapping back. Forexample, memory cells MC1 to MC3 may move further toward state 1 inresponse to voltage pulse VBLWRIT2. In some examples, the senseoperation described in conjunction with memory cell MC0 may be performedafter the writing associated with applying the differential writevoltage pulse VWRITE02 to memory cells MC1 to MC3 is completed. In someexamples, write voltage pulses may be applied to memory cells MC1 to MC3until a sense operation verifies that memory cells MC1 to MC3 are atstate 1. Differential write voltage pulses may be applied in a manner aspreviously described until the memory cells MC1 to MC3 reach state 1.

Using a plurality of pulses to program the memory cells may allow theenergy delivered to the cells to be adjusted during each snapback eventthat may lead to a reduction in the overall energy consumption duringprogramming. It may also allow the overall energy delivered to the cellsto be adjusted by adjusting the number of snapback events. Turning offthe current to a cell during each snapback may also reduce powerconsumption.

In the example of the parallel programming previously described inconjunction with FIG. 10B, the memory cells MC1 to MC3 may be selectedone at a time by their respective snapback events. For example, thememory cells MC1 to MC3 may be selected one at time in order as a resultof their respective threshold voltages (e.g., starting with memory cellMC1 having the lowest threshold voltage (e.g., and/or lowest thresholddelay) and ending with memory cell MC3 having the highest thresholdvoltage (e.g., and/or highest threshold delay)). This can prevent morethan one cell from snapping back at a time. Detection circuitry (e.g.sensing circuitry) detects the snapback of a respective cell, turns thatcell off, and allows the next cell (e.g., with the next highestthreshold voltage) to be snapped back. The parallel programming in theexample of FIG. 10B may act to amortize the individual threshold delaysof memory cells MC1 to MC3 among memory cells MC1 to MC3.

The increase in the voltages of the word line signals VWL1 to VWL3 inresponse to the respective memory cells MC1 to MC3 snapping back may bea consequence of the current limiting by the detection circuitry. Forexample, the current in the respective word lines WL1 to WL3 increasesas a result of the respective memory cells MC1 to MC3 snapping back.This prevents the other cells from snapping back.

FIG. 11 illustrates a portion of a memory array 1100 and associatedcircuitry, in accordance with a number of embodiments of the presentdisclosure. For example, memory array 1100 may be a portion of memoryarray 100. In the example of FIG. 11, sensing circuitries 1130-0 to1130-7 are shared by bit line BL0/word line WL0 to bit line BL7/wordline WL7. For example, word lines WL0 to WL7 are respectivelyselectively electrically coupled to sensing circuitries 1130-0 to 1130-7while bit lines BL0 to BL7 are respectively selectively electricallyisolated from sensing circuitries 1130-0 to 1130-7 and vice versa.

A word line may be selectively electrically coupled to respectivesensing circuitry when data stored by memory cells commonly coupled tothe word line and respectively coupled to different bit lines are beingcompared to an input vector, such as in FIG. 4. A word line may beselectively electrically coupled to respective sensing circuitry whenmemory cells commonly coupled to the bit line and respectively coupledto different word lines are being written, such as in FIG. 10A. A bitline may be selectively electrically coupled to respective sensingcircuitry when memory cells commonly coupled to the bit line andrespectively coupled to different word lines are being compared to aninput vector. A bit line may be selectively electrically coupled torespective sensing circuitry when memory cells commonly coupled to theword line and respectively coupled to different bit lines are beingwritten, such as in FIG. 9A

FIG. 12 is a block diagram of an apparatus, such as an electronic memorysystem 1200, in accordance with a number of embodiments of the presentdisclosure. Memory system 1200 includes an apparatus, such as a memorydevice 1202, and a controller 1204, such as a memory controller (e.g., ahost controller). Controller 1204 might include a processor, forexample. Controller 1204 might be coupled to a host, for example, andmay receive command signals (or commands), address signals (oraddresses), and data signals (or data) from the host and may output datato the host.

Memory device 1202 includes a memory array 1206, such as a cross-pointmemory array, of memory cells. For example, memory array 1206 mayinclude one or more of the memory arrays disclosed herein.

Memory device 1202 includes address circuitry 1208 to latch addresssignals provided over I/O connections 1210 through I/O circuitry 1212.Address signals are received and decoded by a row decoder 1214 and acolumn decoder 1216 to access the memory array 1206. For example, rowdecoder 1214 and/or a column decoder 1216 may include drivers, such asdrivers 550 and 552, as previously described in conjunction with FIG. 5,or drivers 650 and 652, as previously described in conjunction with FIG.6.

Memory device 1202 may sense (e.g., read) data in memory array 1206 bysensing voltage and/or current changes in the memory array columns usingsense/buffer circuitry that in some examples may be read/latch circuitry1220. Read/latch circuitry 1220 may read and latch data from the memoryarray 1206. I/O circuitry 1212 is included for bi-directional datacommunication over the I/O connections 1210 with controller 1204. Writecircuitry 1222 is included to write data to memory array 1206.

Control circuitry 1224 may decode signals provided by controlconnections 1226 from controller 1204. These signals may include chipsignals, write enable signals, and address latch signals that are usedto control the operations on memory array 1206, including data read anddata write operations.

Control circuitry 1224 may be included in controller 1204, for example.Controller 1204 may include, other circuitry, firmware, software, or thelike, whether alone or in combination. Controller 1204 may be anexternal controller (e.g., in a separate die from the memory array 1206,whether wholly or in part) or an internal controller (e.g., included ina same die as the memory array 1206). For example, an internalcontroller might be a state machine or a memory sequencer.

In some examples, controller 1204 may be configured to cause memorydevice 1202 to at least perform the methods disclosed herein, such asthe comparisons, sensing, and writing. In some examples, memory device1202 may include the sense amplifier/feedback circuitries and latches,such as latches 440, 540, 640, disclosed herein. For example, memorydevice 1202 may include the circuitry previously described inconjunction with FIGS. 5 and 6.

As used herein, the term “coupled” may include electrically coupled,directly coupled, and/or directly connected with no intervening elements(e.g., by direct physical contact) or indirectly coupled and/orconnected with intervening elements. The term coupled may furtherinclude two or more elements that co-operate or interact with each other(e.g., as in a cause and effect relationship).

It will be appreciated by those skilled in the art that additionalcircuitry and signals can be provided, and that the memory system 1200of FIG. 12 has been simplified. It should be recognized that thefunctionality of the various block components described with referenceto FIG. 12 may not necessarily be segregated to distinct components orcomponent portions of an integrated circuit device. For example, asingle component or component portion of an integrated circuit devicecould be adapted to perform the functionality of more than one blockcomponent of FIG. 12. Alternatively, one or more components or componentportions of an integrated circuit device could be combined to performthe functionality of a single block component of FIG. 12.

It will be appreciated that the computing functions discussed previouslyin conjunction with the examples of the XOR operation and the examplesof parallel access discussed previously in conjunction with the examplesof parallel sensing and parallel writing may be implementedindependently on general memory devices, such as memory device 1202,that may be used in solid state memories (e.g. that may employresistance-variable memory cells).

Although specific examples have been illustrated and described herein,those of ordinary skill in the art will appreciate that an arrangementcalculated to achieve the same results can be substituted for thespecific embodiments shown. This disclosure is intended to coveradaptations or variations of one or more embodiments of the presentdisclosure. It is to be understood that the above description has beenmade in an illustrative fashion, and not a restrictive one. The scope ofone or more examples of the present disclosure should be determined withreference to the appended claims, along with the full range ofequivalents to which such claims are entitled.

What is claimed is:
 1. A method, comprising: programming a memory cellcoupled to a first signal line and a second signal line from a firstdata state to a second data state by: applying a plurality of voltagedifferential pulses across the memory cell to cause a plurality of snapbacks of the memory cell from a high-impedance state to a low-impedancestate, wherein each respective voltage differential pulse causes arespective snap back of the memory cell from the high-impedance state tothe low-impedance state that incrementally changes a data state of thememory cell from the first data state towards the second data state. 2.The method of claim 1, further comprising applying the plurality ofvoltage differential pulses via a voltage node coupled to the secondsignal line.
 3. The method of claim 2, further comprising, responsive toa respective one of the plurality of snapbacks of the memory cell,decoupling the second signal line from the voltage node for an amount oftime.
 4. The method of claim 3, further comprising, subsequent todecoupling the second signal line from the voltage node for the amountof time, coupling the second signal line to the voltage node.
 5. Themethod of claim 1, wherein each of the plurality of differential voltagepulses has a magnitude greater than a threshold voltage associated withthe first data state of the memory cell.
 6. The method of claim 1,further comprising: applying the plurality of voltage differentialpulses to the first signal line; and a constant voltage to the secondsignal line.
 7. The method of claim 1, further comprising, subsequent toa respective one of the plurality of snap backs, performing a sensingoperation on the memory cell to determine whether the memory cell isprogrammed to the second data state.
 8. An apparatus, comprising: anarray of memory cells, wherein the array of memory cells comprises: afirst memory cell coupled to a first signal line; and a second memorycell coupled to a second signal line, wherein the first and secondmemory cells are commonly coupled to a third signal line; and acontroller coupled to the array of memory cells and configured to: causea first signal pulse having a first polarity to be applied across thefirst memory cell, while the second memory cell is inhibited, inresponse to a first signal indicative of a transition of the firstmemory cell from a non-conductive state to a conductive state, whereinthe first signal pulse causes an incremental change of a data state ofthe first memory cell from a first data state towards a second datastate; and cause a second signal pulse having a second polarity oppositeto the first polarity to be applied across the second memory cell, whilethe first memory cell is inhibited, in response to a second signalindicative of a transition of the second memory cell from thenon-conductive state to the conductive state, wherein the second signalpulse causes an incremental change of a data state of the first memorycell from a third data state towards a fourth data state.
 9. Theapparatus of claim 8, wherein the controller is configured to: cause thefirst signal pulse to be applied across the first memory cell by beingconfigured to cause a first voltage pulse to be applied to the firstsignal line and a constant voltage to be applied to the third signalline; and cause the second signal pulse to be applied across the secondmemory cell by being configured to cause a second voltage pulse to beapplied to the second signal line and a constant voltage to be appliedto the third signal line.
 10. The apparatus of claim 9, furthercomprising: first sensing circuitry coupled to the first signal line andconfigured to decouple the first signal line from a first voltage nodein response to the first signal indicative of the transition of thefirst memory cell from the non-conductive state to the conductive state;and second sensing circuitry coupled to the second signal line andconfigured to decouple the second signal line from a second voltage nodein response to the second signal indicative of the transition of thesecond memory cell from the non-conductive state to the conductivestate.
 11. The apparatus of claim 8, further comprising: a firstdetector coupled to the first signal line and configured to detect thetransition of the first memory cell from the non-conductive state to theconductive state; and a second detector coupled to the second signalline and configured to detect a transition of the second memory cellfrom the non-conductive state to the conductive state.
 12. The apparatusof claim 11, further comprising: a first latch coupled to the firstdetector and configured to: receive a third signal from the firstdetector in response to the first detector detecting the transition ofthe first memory cell from the non-conductive state to the conductivestate; and responsive to receiving the third signal, provide the firstsignal to first sensing circuitry, wherein the first sensing circuitryis configured to decouple the first signal line from a first voltagenode in response to receiving the first signal, and a second latchcoupled to the second detector and configured to: receive a fourthsignal from the second detector in response to the second detectordetecting the transition of the second memory cell from thenon-conductive state to the conductive state; and responsive toreceiving the fourth signal, provide the second signal to second sensingcircuitry, wherein the second sensing circuitry is configured todecouple the second signal line from a second voltage node in responseto receiving the second signal.
 13. The apparatus of claim 11, whereinthe controller is configured to: cause a sense voltage to be appliedacross the first and second memory cells prior to application of thefirst signal pulse to the first signal line and application of thesecond signal pulse to the second signal line; and cause the firstsignal pulse to be applied to the first signal line and the secondsignal pulse to be applied to the second signal line in response to thefirst and second memory cells not transitioning from the non-conductivestate to the conductive state in response to application of the sensevoltage across the first and second memory cells.
 14. A method,comprising: concurrently applying: a first voltage to a first signalline coupled to a first memory cell; the first voltage to a secondsignal line coupled to a second memory cell; and a second voltage to athird signal line commonly coupled to the first and second memory cells,wherein the first memory cell is programmed to a first threshold voltageand the second memory cell is programmed to a second threshold voltagethat is greater than the first threshold voltage; responsive todetecting a snap back event occurring on the first signal line at afirst time in response to the concurrent application of the first andsecond voltages, determining that the first memory cell is programmed toa particular data state; and responsive to not detecting a snap backevent on the second signal line at a second time in response to theconcurrent application of the first and second voltages, determiningthat the second memory cell is programmed to the particular data state.15. The method of claim 14, wherein applying the second voltage to thethird signal line comprises applying a variable voltage with anincreasing magnitude to the third signal line.
 16. The method of claim14, further comprising preventing the first and second memory cells fromexperiencing the snap back event at a same time.
 17. The method of claim14, further comprising increasing a magnitude of the first voltage inresponse to detecting the snap back event on the first signal line. 18.The method of claim 14, further comprising turning off the first voltagein response to detecting the snap back event on the first signal line.19. The method of claim 14, further comprising latching a data valueindicative of the first memory cell being in a different particularstate in response to detecting the snap back event on the first signalline.